IC-NRLF 


355 


A  LABORATORY  MANUAL   IN   CHEMISTRY 


THE  MACMILLAN  COMPANY 

NEW  YORK    •    BOSTON  •    CHICAGO 
DALLAS   •    SAN    FRANCISCO 

MACMILLAN  &   CO.,  LIMITED 

LONDON  '    BOMBAY  •   CALCUTTA 
MELBOURNE 

THE  MACMILLAN  CO.  OF  CANADA,  LTD. 

TORONTO 


A  LABORATORY  MANUAL 
IN  CHEMISTRY 


BY 

WILLIAM   CONGER   MORGAN,  PH.D.  (YALE) 

ASSISTANT   PROFESSOR   AT   THE    UNIVERSITY   OP   CALIFORNIA 
AND 

JAMES  A.  LYMAN,  Pn.D.  (JOHNS  HOPKINS) 

PROFESSOR   OF   CHEMISTRY,    POMONA    COLLEGE 


garfc 
THE   MACMILLAN  COMPANY 

1916 

All  rights  reserved 


COPYRIGHT,  1912, 
BY  THE  MACMILLAN  COMPANY. 


Set  up  and  electrotyped.     Published  July,  1912.     Reprinted 
October,  1912;  February,  September,  1913  ;   March,  1914; 
January,  June,  September,  October,  1915;  February,  August, 
1916. 


Xortoooti 

J.  8.  Cushing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


PREFACE 

THIS  manual  is  intended  to  accompany  "  Chemistry,  an 
Elementary  Textbook,"  by  the  same  authors,  but  it  may 
be  used  advantageously  in  connection  with  any  other  text. 
It  will  prove  interesting  to  teachers  who  wish  to  present 
that  kind  of  chemistry  which  appeals  to  students  because 
of  its  intense  human  interest. 

The  work  outlined  is  intended  for  classes  having  eight 
to  ten  periods  (approximately  45  minutes  each),  per  week 
to  devote  to  the  subject.  It  is  realized  that  this  is  more 
than  can  be  given  in  all  schools,  so  that  a  choice  will  some- 
times be  necessary.  Yet  the  better  students  need  not 
be  tied  down  to  the  amount  of  work  required  of  the 
slower  members.  Where  the  allotted  time  is  too  short 
for  each  student  to  perform  all  the  work,  it  will  prove  in- 
teresting if  some  students  perform  one  experiment  while 
others  are  doing  another,  both  to  be  reported  on  in  the 
classroom  later.  An  abundance  of  material  from  which 
to  choose  is  preferable  to  a  minimum  which  must  be 
amplified. 

The  beginning  student  should  be  given  an  extended 
experimental  introduction  to  the  subject  of  chemistry, 
inasmuch  as  its  methods  of  approach  are  unfamiliar  to  him 
and  many  of  its  facts  beyond  his  personal  experience. 
Hence,  more  time  should  be  devoted  to  experimental  work 
at  the  beginning  of  the  course  than  later. 

Every  teacher  realizes  that  good  lecture  table  experi- 
ments are  quite  as  important  as  any  feature  of  the  course. 
There  are  included,  therefore,  a  goodly  number  of  experi- 

v 

381717 


vi  PREFACE 

ments  intended  to  be  performed  by  the  instructor  while 
the  class  takes  careful  notes.  These  are  generally  too 
difficult  for  the  average  student,  yet  they  cover  points  of 
such  importance  in  the  development  of  the  science  that 
students  should  see  these  demonstrations. 

The  following  experiments  should  be  required  of  all 
students:  1,  2,  5,  10,  18,  19,  21,  22,  24,  26,  28,  29,  30,  34, 
36,  39,  41  or  42,  44,  46,  49,  50,  51,  52,  53,  54,  57,  58,  59, 
61,  64,  65,  67,  69,  72,  73.  As  many  others  should  be  per- 
formed as  time  will  permit. 

Suggestions  for  the  improvement  of  this  manual  from 
teachers  who  have  used  it  with  classes  will  be  appreciated 

by  the  authors. 

W.  C.  MORGAN. 

BERKELEY,  1912.  J.  A.  LYMAN. 


TABLE   OF   CONTENTS 

PAGE 

PREFACE v 

SUGGESTIONS  TO  TEACHERS x 

SUGGESTIONS  TO  STUDENTS *   .  xii 

PRELIMINARY  EXERCISES 

BUNSEN  BURNER 1 

MANIPULATION  OF  GLASS  TUBING       .....  2 

EXPERIMENT 

1.  CHEMICAL  AND  PHYSICAL  CHANGES 5 

2.  COMPOUNDS  AND  MIXTURES 6 

3.  WHICH  REACT  MORE  READILY,  GASES,  LIQUIDS,  OR  SOLIDS  ?  8 

4.  How  CHEMICAL  CHANGES  ARE  BROUGHT  ABOUT       .        .  9 

5.  WHAT  is  FLAME  ? 12 

^6.  WHEN  A  SUBSTANCE  BURNS,  is  THERE  ANY  CHANGE  IN 

WEIGHT? 13 

-7.   Is  THE  TOTAL  WEIGHT  OF  MATTER  AFTER  A  CHANGE  THE 
SAME  AS  THE  TOTAL  WEIGHT  OF  MATTER  BEFORE  THE 

CHANGE? 15 

£.   THE  GAS  THAT  MAKES  A  FIRE  BURN 17 

9.   HOW  MAY  THE  SPEED  OF  REACTIONS  BE  INCREASED?      .  18 

AQ.   PREPARATION  AND  PROPERTIES  OF  OXYGEN       .        .        .  19 

-11.   OXYGEN  CONSUMED  DURING  COMBUSTION  ....  21 

12.  HEAT  EVOLVED  DURING  SLOW  OXIDATION  LEADS  TO  SPON- 

TANEOUS COMBUSTION 24 

13.  KINDLING  TEMPERATURE 24 

14.  DIFFUSION 26 

15.  DECOMPOSITION  OF  WATER  BY  ELECTRICITY      ...  28 

16.  DECOMPOSITION  OF  WATER  BY  METALS     ....  31 

17.  ACTION  OF  METALS  ON  ACIDS .34 

18.  PREPARATION  AND  PROPERTIES  OF  HYDROGEN  ...  35 
-19.   OXIDATION  AND  REDUCTION 38 

20.   NASCENT  STATE 39 

vii 


vm  CONTENTS 

EXPERIMENT  PAQB 

21.  DECANTATION,  FILTRATION,  AND  DISTILLATION         .        .  40 

22.  How  HEAT  AFFECTS  SOLUBILITY 43 

23.  SUPERSATURATION 44 

24.  SOLUTIONS  OF  GASES 45 

25.  CRYSTALLIZATION 46 

26.  WATER  IN  CRYSTALS 47 

27.  PURIFICATION  BY  CRYSTALLIZATION 50 

28.  REACTIONS  RUN  TO  EQUILIBRIUM  UNLESS  PREVENTED  BT 

SOME  FACTOR 51 

29.  HYDROGEN  CHLORID 55 

30.  CHLORIN 57 

31.  BLEACHING  WITH  HYPOCHLOROUS  ACID       ....  60 

32.  PERCENTAGE  OF  OXYGEN  IN  POTASSIUM  CHLORATE          .  62 

33.  DETERMINATION  OF  THE  VOLUME  RATIO  IN  WHICH  HY- 

DROGEN AND  OXYGEN  COMBINE 65 

34.  BASES 66 

35.  NITROGEN  —  ITS  PREPARATION  AND  PROPERTIES       .        .  69 

36.  NITRIC  ACID 71 

37.  NITROGEN  MONOXID,  OR  NITROUS  OXID    ....  72 

38.  NITROGEN  DIOXID,  OR  NITRIC  OXID 74 

39.  AMMONIA 76 

40.  DECOMPOSITION  OF  AMMONIA  BY  ELECTRICITY  ...  78 

41.  EQUIVALENT  OF  MAGNESIUM 79 

42.  EQUIVALENT  OF  SODIUM 80 

43.  PREPARATION  OF  AN  ACID  SALT 81 

44.  CARBON 82 

J    45.  MANUFACTURE  OF  ILLUMINATING  GAS        ....  84 

46.  CARBON  DIOXID  AND  CARBONIC  ACID        ....  85 

47.  CARBON  MONOXID 87 

48.  BURNING  AND  SUPPORTING  COMBUSTION     ....  89 

49.  FLAMES 90 

50.  HYDROCARBONS 92 

51.  ALCOHOL  AND  ACETIC  ACID  BY  FERMENTATION         .        .  94 
s.  52.   SOAP  96 


CONTENTS  ix 

EXPERIMENT  PAGE 

53.  CONSTITUENTS  OF  FOODS       .......  97 

54.  HALOGEN  GROUP 101 

55.  BROMIN 102 

56.  IODIN 104 

57.  SULFUR 105 

58.  HYDROGEN  SULFID 107 

59.  SULFUR  DIOXID  AND  SULFUROUS  ACID       ....  109 

60.  SULFUR  TRIOXID  AND  SULFURIC  ACID         .        .        .        .111 

61.  PHOSPHORUS 112 

62.  PHOSPHIN         .                114 

63.  ARSIN  AND  STIBIN 115 

64.  ELEMENTS  THAT  ACT  BOTH  AS  ACID-FORMERS  AND  BASE- 

FORMERS    116 

65.  REDUCTION  OF  METALS  FROM  THEIR  ORES        .        .        .  117 

66.  BORIC  ACID  AND  BORAX  BEAD  TESTS         .        .        .        .119 

67.  ALUM  FROM  CLAY 121 

68.  DYES  AND  MORDANTS 122 

69.  HARD  WATER  AND  HOW  TO  SOFTEN  IT       ....  124 

70.  FLAME  TESTS  AND  COLORED  FIRE      .                .        .        .  126 

71.  MANUFACTURE  OF  POTASSIUM  NITRATE     ....  127 

72.  WASHING  SODA,  BAKING  SODA,  AND  BAKING  POWDERS  .  128 

73.  REPLACEMENT  OF  ONE  METAL  BY  ANOTHER    .        .        .  130 

74.  REACTIONS  OF  SILVER  SALTS  IN  PHOTOGRAPHY         .        .  131 

75.  EFFECT  OF  OXIDATION  ON  THE  PROPERTIES  OF  ELEMENTS  132 

76.  BLUEPRINTS  AND  THEIR  REACTIONS- 134 

77.  IDENTIFICATION  OF  SIMPLE  SUBSTANCES     ....  136 

LISTS  OF  CHEMICALS  AND  SUPPLIES 139 

MATERIALS  TO  BE  OBTAINED  LOCALLY  AS  NEEDED  .        .        .  140 

INDIVIDUAL  APPARATUS 141 

APPARATUS  FOR  GENERAL  USE    .  142 


SUGGESTIONS  TO  TEACHERS 

IN  the  following  experiments  the  shelf  reagents  are 
supposed  to  be  about  10  per  cent  solutions ;  say  100  g. 
of  the  solute  in  a  liter  of  water.  Concentrated  reagents 
are  of  the  specific  gravities  given  below  and  the  dilute 
reagents  are  made  as  specified. 

Hydrochloric  acid,  Sp.  Gr.  1.19.     Pour  into  4  volumes  of 

water. 

Nitric  acid,  Sp.  Gr.  1.42.     Pour  into  5  volumes  of  water. 
Sulfuric  acid,  Sp.   Gr.    1.84.     Pour   into    6   volumes    of 

water. 
Ammonium  hydroxid,  Sp.  Gr.  0.90.     Pour  into  4  volumes 

of  water. 

A  pneumatic  trough  may  be  made  of  a  deep  baking 
pan  and  a  single  muffin  tin  with  two 
round  holes  cut  in  it  by  any  tinsmith, 
as  shown  in  Fig.  A.  Painted  with 
asphalt  varnish  they  will  last  for- 
ever. Fl<>. 

Capsules  for  sodium  may  be  purchased,  or  made  by 
cutting  f-inch  brass  tubing  (wall  •£%  inch)  into  1-inch 
lengths  and  soldering  a  disk  of  brass  air-tight  on  to  one 
end.  A  10-inch  piece  of  copper  wire,  one  end  wrapped 
several  times  firmly  about  the  capsule,  serves  as  a  holder. 

Rubber  stoppers  are  much  better  than  corks.  Only 
best  quality  rubber  goods  should  be  purchased;  the 
poorer  grades  oxidize  quickly  and  become  hard.  Good 
rubber  stoppers  that  have  become  hard  may  be  softened 
by  boiling  in  a  10  per  cent  NaOH  solution. 


SUGGESTIONS  TO  TEACHERS  xi 

To  cut  glass  tubing  of  large  diameter,  make  a  short 
scratch  with  a  file.  Fold  a  filter  paper  so  that  its  edges 
are  parallel  and  moisten  it.  Wrap  such  a  piece  about  the 
tube  each  side  of  the  mark,  leaving  a  space  about  £  of 
an  inch  wide  exposed.  Heat  this  space  in  a  blowpipe 
with  a  fine  flame,  rotating  the  tube  until  it  breaks;  or 
touch  the  hot  ring  with  a  drop  of  water. 

To  avoid  repeated  weighings  on  the  part  of  students 
(see  Exp.  22)  make  small  measures  out  of  glas?  tubing  of 
appropriate  size  sealed  at  one  end.  Weigh  out  1  g.  (if 
this  is  the  desired  amount)  of  the  substance,  insert  in  the 
tube,  and  jar  it  until  the  powder  lies  in  the  closed  end. 
Cut  off  that  part  of  the  tube  filled  by  the  powder,  affix  to 
a  wooden  splint  by  means  of  glue  and  tough  paper,  and  a 
•  serviceable  measure  has  been  made. 

Magnesium  ribbon  usually  runs  uniform  and  can  be 
measured  more  accurately  than  weighed  by  students  (see 
Exp.  41). 

The  larger  schools  will  find  it  very  convenient  to  keep 
in  the  laboratory  three  Kipp  generators,  one  fitted  for 
hydrogen,  one  for  hydrogen  sulfid,  and  one  for  carbon 
dioxid.  An  oxone  generator  for  oxygen  is  very  handy. 

If  a  gas  holder  is  not  available,  a  satisfactory  method  of 
handling  small  volumes  of  gas  is  illustrated  in  Exps.  47 
and  59. 

It  is  advisable  to  keep  on  hand  in  the  laboratory  a 
bottle  containing  olive  oil  and  lime  water  (equal  parts) 
to  be  used  on  burns.  Shake  thoroughly  "before  applying 
to  the  burn  and  bandage  to  keep  from  the  air.  A  dilute 
solution  of  baking  soda  may  be  substituted  for  the  lime 
water. 


SUGGESTIONS   TO  STUDENTS 

WHEN  you  enter  the  laboratory,  learn  the  names  of  the 
apparatus  and  see  that  you  have  the  complete  list.  If 
not,  report  it  to  the  instructor. 

Wash  your  apparatus  at  the  beginning  and  keep  it 
scrupulously  clean  and  your  desk  neat.  Slovenly  work 
causes  experiments  to  go  wrong,  necessitating  repetition. 
When  work  is  completed  for  the  day,  put  away  the  ap- 
paratus and  clean  the  desk. 

Vessels  of  thin  glass  may  be  heated  with  safety.     With 
thick   glass,   uneven   heating  causes  irregular  expansion 
and  breaking.     Always  place  a  wire 
gauze  between  a  beaker  or  flask  and  the 
flame.     Test  tubes  and  porcelain  may 
be  heated  in  the  flame.  Never  heat  glass 
containing  a  liquid  at  the  surface  of 
the  liquid.     It  is  sure  to  break.     Heat 
as  shown  in  Fig.  B,  using  a  strip  of 
paper  several  times  folded  as  a  substi- 
tute for  a  test  tube  holder,  if  necessary. 
Shake  the  test  tube  continually  while 
heating  to  prevent  explosive  boiling. 
Direct  the  mouth  of  the  test  tube  away  from  yourself 
and  your  neighbor  as  well. 

Before  attempting  to  insert  glass  into  rubber,  wet  both. 
Don't  push  or  pull,  but  twist  a  glass  tube  into  position  in 
a  rubber  stopper,  thus  avoiding  cuts  from  broken  glass. 

Before  boring,  soften  a  cork  by  rolling  under  the  hand 
or  foot.  Select  a  borer  one  .size  smaller  than  the  tube 
to  be  fitted.  Place  the  cork  against  a  board  and  with  a 
gentle  pressure  rotate  it  until  it  cuts  neatly  through.  Do 
not  attempt  to  push  it  through,  as  this  makes  ragged  holes. 

xii 


SUGGESTIONS  TO  STUDENTS  xin 

Be  sparing  in  the  use  of  reagents.  Too  much  is  often 
as  detrimental  to  good  work  as  too  little.  If  too  much  of 
a  liquid  reagent  has  been  removed,  throw  the  excess 
away.  Never  pour  it  back  into  the  bottle.  The  quanti- 
ties of  reagents  specified  are  usually  only  approximate 
and  meant  to  be  estimated  rather  than  weighed  or  meas- 
ured. Learn  to  know  how  much  1  and  5  g.  of  ordinary 
substances  are.  An  ordinary  test  tube  (6  x  f  inches) 
holds  30  ccm.  Learn  what  5  and  10  ccm.  are. 

Never  lay  the  stopper  of  a  reagent 
bottle  down  on  the  shelf  or  desk,  thus 
contaminating  it  with  other  sub- 
stances. In  obtaining  reagents  from 
bottles,  turn  the  palm  of  the  hand  up 
and  remove  the  stopper  by  grasping 
between  the  fingers  and  holding  as 
FIG.  C.  shown  in  Fig.  c. 

Never  taste  any  reagent  unless  definitely  told  to  do  so, 
for  most  chemicals  are  poisons.  In  smelling,  waft  the 
fumes  toward  the  nose  with  the  hand. 

Dilute  acids  and  solutions  of  reagents  are  always  meant 
unless  concentrated  acids  or  solid  reagents  are  specified. 

Always  place  the  substance  to  be  weighed  on  a  piece 
of  paper  on  the  balance,  never  on  the  balance  pan  itself. 

To  insert  a  powder  neatly  into  a  test  tube,  place  it  on 
one  end  of  a  narrow  piece  of  paper  folded  lengthwise. 
Insert  the  paper  into  the  test  tube,  turn  upright  and  jar 
the  powder  from  the  paper. 

Throw  only  liquids  in  sinks;  all  paper  and  other  solids 
in  jars  or  boxes.  After  pouring  acids  into  sinks,  flush 
out  with  water. 

All  temperatures  are  Centigrade;  volumes  and  weights 
are  in  Metric  Measures,  familiarity  with  which  is  presup- 
posed on  the  part  of  all  students. 

(Hood)  means  perform  under  a  hood. 


LABOKATORY  MANUAL  IN  CHEMISTKY 

PRELIMINARY  EXERCISES 

THE   BUNSEN  BURNER 

Apparatus.  Bunsen  Burner  and  about  60  cm.  of  rubber 
tubing.  Ring  stand  or  tripod.  Wire  gauze.  Beaker. 

NOTE.  This  burner  was  first  made  by  the  distinguished  German 
scientist,  Bunsen.  Probably  no  other  invention  has  done  so  much  to 
facilitate  work  in  the  laboratory. 

Procedure,     (a)   The  parts  of  the  burner  and  their  uses. 

Unscrew  the  tube  of  the  burner,  and  notice  the  various 
parts.  Then  put  the  parts  together  again,  using  a  little 
oil  if  the  joints  appear  rusted,  and  connect  the  burner 
to  the  gas  pipe  by  means  of  the  rubber  tubing.  Having 
turned  on  the  gas,  light  it  by  holding  a  burning  match 
close  to  the  burner  tube  about  1  cm.  below  the  top. 

Turn  the  ring  near  the  base  of  the  burner  until  its 
openings  coincide  with  the  openings  in  the  tube.  This 
allows  air  to  mix  with  the  gas  before  the  latter  reaches 
the  flame  above.  Turn  the  ring  until  the  air  is  shut  off. 
What  changes  are  brought  about  in  the  flame  by  varying 
the  supply  of  air  ?  Ascertain  by  means  of  a  wire  or  glass 
rod  which  flame  is  hottest  and  which  deposits  soot. 
Which  flame  is  most  suitable  for  laboratory  purposes? 
Hold  the  wire  in  different  parts  of  the  blue  flame.  Which 
is  the  hottest  part  of  the  flame  ? 

While  the  flame  is  burning  blue,  hold  a  lighted  match 
against  one  of  the  holes.  The  flame  " strikes  buck"  and 

B  1 


LABORATORY  MANUAL  IN  CHEMISTRY 

burns  at  the  base.  Notice  the  odor, 
the  character  of  this  flame  and  the  tem- 
perature of  the  burner  tube.  This  flame 
is  unsuitable  for  laboratory  purposes. 
If  a  burner  during  use  strikes  back,  the 
indication  is  that  there  is  too  much  air 
mixed  with  the  gas.  To  prevent  the 
trouble,  turn  on  more  gas  or  shut  off 
some  of  the  air.  If  a  burner  strikes 
back,  a  sharp  blow  with  the  fist  on  the 
rubber  tubing  will  usually  restore  the 
flame  to  its  proper  condition.  If  not,  the  gas  must  be 
shut  off,  after  which  it  may  be  lighted  again. 

(5)   The  use  of  wire  gauze. 

Place  the  wire  gauze  on  the  tripod,  and  set  the  lighted 
Bunsen  burner  below  the  gauze.  Notice  how  the  gauze 
moderates  the  heat  by  distributing  it  over  a  larger  sur- 
face, due  to  the  fact  that  metals  are  good  conductors  of 
heat.  A  beaker  of  water  may  be  boiled  on  the  hottest 
part  of  the  gauze  without  danger  of  breaking  (see  Fig.  1). 


FIG.  1. 


THE  MANIPULATION  OF  GLASS  TUBING 

Materials.  Glass  tubing,  outside  diameter  about  5  mm. 
Rubber  tubing,  inside  diameter  a  little  less  than  the  out- 
side diameter  of  the  glass  tubing.  ^  ,.  „  -^ 

\Y"»  t        \    "liW 

Apparatus.     A  sharp,  three-cornered  file.     A   \.  \  \7 
Bunsen   burner  and   wing  top  (Fig.   2)  ;    or  a      ^j 
common  fishtail  gas  burner.  FJG.  2. 

Procedure,     (a)   To  cut  glass  tubing. 

Lay  a  piece  of  glass  tubing  on  the  table,  and  at  the 
place  where  it  is  to  be  cut  make  a  scratch  with  the  file. 
Then  grasp  the  tube  firmly  with  a  hand  on  either  side  of 


PRELIMINARY  EXERCISES  3 

the  mark,  and  press  with  the  tips  of  the  thumbs  opposite 
the  scratch.     The  tube  will  usually  break  evenly  across. 

(6)   To  smooth  the  end  of  a  glass  tube. 

Notice  that  the  broken  end  of  a  glass  tube  is  very  sharp 
and  would  cut  any  soft  object  with  which  it  comes  in  con- 
tact. Round  off- the  sharp  edges  by  heating  in  a  Bunsen 
flame,  rotating  the  tube  until  the  glass  begins  to  melt 
slightly.  Where  it  is  not  desirable  to  heat  the  tube,  the 
sharp  ends  may  be  smoothed  by  sandpaper  or  by  the  flat 
side  of  a  file.  • 

(c)   To  seal  glass  tubing. 

Heat  a  piece  of  glass  tubing  about  30  cm.  long  about 
5  cm.  from  one  end  in  the  flame  of  the  Bunsen  burner, 
rotating  it  so  that  it  may  be  evenly 
heated.  When  it  becomes  very  soft, 
gently  draw  it  out  as  shown  in  Fig.  3. 
Allow  the  tube  to  cool,  then  scratch  with  a  file  at  the 
points  A  and  J5,  and  break  as  previously  directed.  Hold 
the  narrow  end  of  the  longer  piece  in  the  flame,  rotating 
it  until  the  edges  melt  together  and  the  end  is  closed. 
Repeat  the  drawing  out,  cutting,  and  sealing  on  the  other 
end  of  the  tube  and  you  have  made  a  stirring  rod. 

(cT)   To  lend  glass  tubing. 

Hold  a  piece  of  glass  tubing  lengthwise  in  the  flattened 
flame  of  a  fishtail  burner  or  Bun- 
sen  burner  with  wing  top,  as 
shown  in  Fig.  4,  so  that  about 
5  cm.  of  the  tubing  is  heated 
where  the  bend  is  to  be.  Rotate 
the  tube  so  that  it  may  be  evenly 
heated.  When  it  is  so  hot  that 
FIG.  4.  it  bends  readily,  remove  it  from 


4  LABORATORY  MANUAL  IN  CHEMISTRY 

the  flame  and  immediately  bend  it  into  the  desired  shape, 
holding  it  in  that  position  until  the  glass  hardens.  If  the 
Bunsen  burner  has  been  used,  turn  off  the  supply  of  air, 
and  by  holding  the  tube  in  the  yellow  flame  allow  the  bend 
to  become  covered  with  soot.  This  allows  the  tube  to 
cool  slowly,  thus  preventing  unequal  strains  in  the  glass. 
This  slow  cooling,  called  "  annealing,"  makes  the  glass 
less  liable  to  break. 

If  the  bend  is  not  smooth  and  even  like  Fig.  5  A,  the 
tubing  was  not  heated  through  a  sufficient  length,  result- 
ing in  flattening,  B ;  or  else  it  was  not  heated  uniformly, 


I  N  C  H  Eg. 

ABC 

FIG.  5. 

producing  kinked  and  unsightly  bends  which  usually  break 
readily,  O.  Never  attempt  to  make  a  bend  by  using  the 
ordinary  flame  of  the  Bunsen  burner. 

If  a  bend  is  needed  near  the  end  of  a  piece  of  tubing, 
make  the  bend  in  a  longer  piece  that  may  be  handled 
readily  and  afterwards  cut  off  such  portions  as  are 
unnecessary. 

Make  exit  and  delivery  tubes  of  the  shapes  and  sizes 
indicated  in  A,  D,  and  E,  smoothing  the  ends  in  the  flame, 
and  preserve  for  future  use.  Three  pieces  like  A  will  be 
needed  in  some  experiments. 


EXPERIMENTS 

EXP.  1.    CHEMICAL  AND  PHYSICAL  CHANGES 

Materials.  Colorless  rock  candy.  Platinum  wire. 
Magnesium  ribbon  or  wire.  Wooden  splints. 

Apparatus.  A  mortar  and  pestle,  small  beaker  and  a 
test  tube.  A  Bunsen  burner,  ring  stand  or  tripod,  and 
gauze.  A  test  tube  holder. 

Procedure.  Examine  a  specimen  of  rock  candy,  notic- 
ing its  properties,  such  as  color,  taste,  hardness,  and  crys- 
talline form.  Judging  from  its  taste,  of  what  does  the 
rock  candy  consist  ? 

1.  In  a  clean  mortar  pulverize  5-10  g.  of  rock  candy. 
Note  any  change  in  properties.     See  whether  the  charac- 
teristic property,  i.e.  the  taste  of  sugar,  has  been  changed 
by  the  grinding.     Is  the  substance  still  sugar  ? 

2.  Partly  fill  the  beaker  with  warm  water  and  dissolve 
a  little  of  the  pulverized  rock  candy  in  it,  stirring  with  a 
glass  rod  as  the  candy  is  added.     What  properties  are 
changed?     Taste  the  solution.     Has  the  sugar  been  de- 
stroyed, or  is  it  still  in  existence? 

3.  Heat  some   of  the  powdered  rock  candy  in  a  dry 
test  tube,  applying  the  heat  gently  at  first,  noting  carefully 
the  progressive  changes.     When  no  further  change  takes 
place  even  at  a  more  intense  heat,  remove  the  test  tube 
and  its  contents  from  the  flame.     When  the  tube  is  cool, 
break  it  and   examine  the  substance  within.      Taste  it. 
Will  it  dissolve  in  water?     Notice  its  color  and  softness. 
See  whether  it  will  burn.     Does  the  sugar  still  exist? 
What  does  the  new  substance  resemble? 

6 


6  LABORATORY  MANUAL  IN  CHEMISTRY 

Compare  the  change  brought  about  in  3  with  the 
changes  in  1  and  2,  telling  how  they  differ  in  their  effect 
on  the  sugar.  The  change  in  1  and  2  is  physical.  The 
change  in  3  is  chemical. 

4.  Heat  successively  in  the  flame  of  the  burner  pieces 
of  wood,  platinum  wire,  magnesium  wire  or  ribbon,  and 
glass.  Compare  the  properties  of  the  substances  before 
heating  with  their  properties  after  heating,  and  decide  in 
each  case  whether  the  change  is  chemical  or  physical. 
Give  reason  for  your  answer  in  each  case. 

EXP.  2.    COMPOUNDS  AND  MIXTURES 

Materials.     Powdered  iron.*    Sulfur.    Carbon  disulfid.t 

Apparatus.  Test  tubes.  Magnifying  glass.  Magnet. 
Watch  glass  or  evaporating  dish. 

Procedure,     (#  )   The  properties  of  sulfur. 

Note  the  visible  properties  of  a  piece  of  sulfur,  exam- 
ining the  powdered  material  with  a  magnifying  glass. 
Touch  it  with  a  magnet. 

Burn  a  small  bit  of  sulfur  and  cautiously  notice  the 
familiar  odor. 

Drop  a  small  piece  of  sulfur  into  3—5  ccm.  of  carbon 
disulfid  in  a  test  tube  and  shake  for  about  5  minutes. 
(CAUTION  :  Do  not  bring  carbon  disulfid  near  a  flame,  as 
its  vapor  is  very  inflammable  !)  Does  the  sulfur  seem  to 
dissolve?  Pour  off  the  liquid  from  any  undissolved  sul- 
fur into  a  watch  glass  or  evaporating  dish  and  allow  it  to 
evaporate  under  a  hood.  If  any  sulfur  is  left  upon  the 

*  Iron  filings  do  not  work  as  satisfactorily  as  powdered  iron,  which 
may  be  purchased  from  any  chemical  dealer. 

t  Because  of  the  way  in  which  it  is  prepared  (see  text,  p.  250)  com- 
mercial carbon  disulfid  usually  contains  sulfur  dissolved  in  it.  For  this 
experiment  the  carbon  disulfid  should  be  distilled  to  free  it  from  sulfur 
and  other  impurities. 


EXPERIMENTS  7 

watch  glass,  it  must  have  been  dissolved  in  the  liquid. 
Did  any  of  the  sulfur  dissolve  in  the  carbon  disulfid? 
This  is  a  general  method  of  testing  whether  a  substance 
is  soluble  in  a  liquid. 

What  are  some  of  the  characteristic  properties  of  sulfur  ? 

(5)   The  properties  of  iron. 

Examine  some  iron  powder  under  a  magnifying  glass 
and  touch  it  with  a  magnet. 

Ascertain  whether  iron  powder  will  dissolve  in  carbon 
disulfid,  proceeding  as  with  sulfur. 

What  are  some  of  the  characteristics  of  iron  powder? 

(c)   The  characteristics  of  a  mixture  of  iron  and  sulfur. 
Stir  together  5  g.  of  powdered  sulfur  and  7  g.  of  iron 
powder.     What  is  the  color  of  the  new  powder. 

1.  Bring   a   magnet   to   some  of   the   mixture.      Does 
the  iron  still  exist  ? 

2.  Shake  a  pinch  of  the  mixture  in  a  test  tube  with 
5  ccm.  of  carbon  disulfid,  carefully  pour  off  the  liquid  from 
the  undissolved  material  and  evaporate  on  a  watch  glass. 
What  is  the  residue  left  on  the  watch  glass?     Does  the 
sulfur  still  exist  in  the  mixture  ?     What  is  left  in  the 
test  tube  ? 

From  the  above  tests,  do  the  iron  and  the  sulfur  appear 
to  retain  their  identity  when  they  are  mixed  ?  Is  there 
any  evidence  indicating  that  any  change  has  taken  place  ? 

(jd)    The  properties  of  a  compound  of  iron  and  sulfur. 

Heat  the  rest  of  the  mixture  of  iron  and  sulfur  in  a 
test  tube  with  a  small  flame.  When  the  mass  begins  to 
glow  like  a  red-hot  coal,  remove  it  from  the  flame,  as 
the  change  will  continue  without  further  heating.  Lay 
the  tube  down  on  its  side  to  cool.  There  is  probably  a 
little  melted  sulfur  a  part  of  the  way  up  the  inside  of  the 


8  LABORATORY  MANUAL  IN  CHEMISTRY 

test  tube.  Do  not  allow  this  to  run  down  and  mingle 
with  the  substance  at  the  bottom.  When  the  tube  is 
cool,  break  it  open  and  examine  with  a  magnifying  glass 
the  substance  left  where  the  glow  had  been.  Can  the 
iron  or  the  sulfur  be  seen  ?  Touch  a  flame  to  some  of  the 
substance.  Does  it  burn  ?  See  if  any  sulfur  can  be 
dissolved  out  of  it  by  means  of  carbon  disulfid.  Bring 
a  magnet  to  a  lump  of  the  substance.  Can  you  detect 
either  the  iron  or  the  sulfur  in  the  new  substance  ? 

Through  what  kind  of  a  change  have  the  iron  and 
the  sulfur  passed?  The  product  is  a  chemical  compound. 
How  can  you  distinguish  a  mixture  from  a  compound  ? 

EXP.  3.    WHICH  REACT  MORE  READILY,  GASES,  LIQUIDS 
OR  SOLIDS? 

Materials.  Cone,  ammonium  hydroxid,  hydrochloric 
acid  and  sulfuric  acid.  Alcohol.  Potassium  chlorate. 
Sulfur.  Cream  of  tartar  (hydrogen  potassium  tartrate). 
Baking  soda  (hydrogen  sodium  carbonate). 

Apparatus.  Graduate.  Mortar  and  pestle.  Two  small 
evaporating  dishes  or  watch  glasses.  Test  tube. 

Procedure,    (a)    G-ases. 

In  a  watch  glass  or  evaporating  dish  put  about  5  ccm. 
of  cone,  ammonium  hydroxid  solution  and  in  another 
put  the  same  quantity  of  cone,  hydrochloric  acid.  Place 
the  two  liquids  side  by  side  so  that  the  gases  escaping 
from  them  may  mix.  If  the  liquids  are  warmed,  the 
gases  escape  more  readily.  Catch  some  of  the  new 
substance  on  a  piece  of  cold  glass.  What  evidence  do 
you  observe  that  a  chemical  change  is  taking  place  ? 

(5)    Liquids. 

Measure  10  ccm.  of  alcohol  into  a  test  tube,  and  to  it 
add  in  small  portions  an  equal  volume  of  cone,  sulfuric 


EXPERIMENTS  9 

acid.  A  change  of  temperature  usually  accompanies  a 
chemical  change.  Do  you  notice  any?  Is  there  any 
visible  new  product  to  show  that  a  chemical  change  has 
taken  place  ? 

O)    Solids. 

1.  Pulverize  finely  in  jsej^ajrate  *  mortars  2  g.  of  potas- 
sium chlorate  and  1  g.  of  sulfur.      (CAUTION  :   Do   not 
grind  the  two  substances  together  !)     Mix  the  powders 
thoroughly  on  a  piece  of  paper,  using  the  fingers  only. 
Is  there  evidence  of  chemical  action  ?     Save  the  powder 
for  the  next  exercise. 

2.  Thoroughly  mix  together  4  g.  of  cream  of  tartar 
and  2  g.  of  baking  soda,  both  finely  powdered.     Is  there 
any  evidence  of  a  chemical  reaction  ?     Save  the  mixture 
for  the  next  exercise.     State  the  relative  readiness  with 
which  gases,  liquids  and  solids  react. 

EXP.  4.    HOW  CHEMICAL  CHANGES  ARE  BROUGHT  ABOUT 

Materials.  The  mixtures  (potassium  chlorate  with  sul- 
fur, and  cream  of  tartar  with  baking  soda)  from  the  last 
exercise.  Blue  print  paper.  Copper  sulfate  solution. 
Sulfuric  acid.  Zinc  dust.  Powdered  sulfur. 

Apparatus.  A  strip  of  zinc  and  of  copper  about  5  cm. 
wide  and  10  cm.  long.  Two  copper  wires  about  25  cm. 
long.  Two  platinum  wires  5  cm.  long.  Beakers.  Two 
dry  cells.  A  compass. 

Procedure,     (a)  By  mechanical  means. 

Place  the  mixture  of  potassium  chlorate  and  sulfur  on 
a  flat  piece  of  iron  or  stone,  and  hit  it  a  sharp  blow  with 
a  hammer.  What  evidence  is  there  of  chemical  action  ? 

*Some  students  may  pulverize  the  potassium  chlorate,  others  the 

. 


10          LABORATORY  MANUAL  IN  CHEMISTRY 

Hit  the  head  of  a  parlor  match  a  light  blow,  and  compare 
the  results.  Do  you  think  these  reactions  are  endothermic 
or  exothermic  ? 

(5)  By  light. 

Lay  a  piece  of  blue  print  paper,  sensitive  side  up,  on  a 
book,  put  on  the  paper  several  coins,  flat  keys,  or  similar 
opaque  objects,  and  expose  the  whole  to  bright  sunlight 
until  the  parts  of  the  paper  on  which  the  light  shines 
have  taken  a  bronzed  appearance.  Then  remove  the 
opaque  objects  from  the  paper,  notice  the  appearance  of 
the  unexposed  spots,  and  wash  the  paper  in  water.  What 
evidence  is  there  that  a  chemical  change  has  taken  place  ? 
In  making  photographs  does  the  picture  get  any  darker 
after  it  is  removed  from  the  sunlight?  Is  the  reaction 
endothermic  or  exothermic  ? 

(js)  By  electricity.* 

"  Make  a  hole  near  one  end  of  the  zinc  and  copper  strips 
and  connect  the  two  by  means  of  a  copper  wire.  Place 
the  metals  in  sulfuric  acid,  taking  care  that  they  do  not 
touch  each  other. j-  What  happens?  What  evidence  of 
a  chemical  reaction  do  you  see  ? 

The  chemical  energy  liberated  by  the  reaction  is  con- 
verted into  electrical  energy  by  this  apparatus  and  an 
electric  current  is  said  to  flow  through  the  wire.  Bring 
a  compass  near  the  wire  and  note  the  indication  that  a 
current  is  flowing,  holding  the  compass  first  above,  then 
below  the  wire. 

The  current  produced  by  this  little  cell  is  not  suffi- 
ciently strong.  For  the  following  experiment  substitute 
two  dry  cells  arranged  in  series. 

*  This  part  of  the  experiment  may  be  performed  by  the  instructor  be- 
fore the  class. 

t  The  metals  may  be  kept  from  coming  in  contact  by  tying  them  with 
a  piece  of  string  on  opposite  sides  of  a  strip  of  shingle  or  thin  wood. 


EXPERIMENTS  11 

Connect  the  copper  wires  to  the  poles  of  the  battery. 
Without  allowing  the  wires  to  come  into  contact  with 
each  other,  touch  them  to  the  tongue  and  "  taste  the  elec- 
tric current." 

Connect  platinum  wires  to  the  ends  of  the  copper  wires. 
Dip  the  platinum  wires  into  copper  sulfate  solution  for 
1-2  minutes.  What  evidence  is  seen  that  the  passage  of 
an  electric  current  through  the  solution  has  caused  a 
chemical  change  ?  On  which  wire  is  the  deposit  ?  What 
is  it  ?  Is  the  reaction  which  has  taken  place  analysis  or 
synthesis  ? 

Disconnect  one  of  the  copper  wires  from  the  battery. 
Then  dip  the  platinum  wires  farther  into  the  copper  sul- 
fate solution,  and  ascertain  if  there  is  any  chemical  change 
when  the  circuit  is  broken  and  the  supply  of  electrical 
energy  is  stopped.  Is  the  reaction  with  the  copper  sulfate 
exothermic  or  endothermic  ? 

(c?)  By  solution. 

Pour  a  little  water  on  the  mixture  of  cream  of  tartar 
and  baking  soda,  so  that  the  ingredients  can  dissolve. 
What  evidence  is  there  of  chemical  action  ?  Is  the  reac- 
tion exothermic  or  endothermic  ? 

(e)  By  heat. 

Mix  7  g.  of  zinc  dust  with  4  g.  of  powdered  sulfur.  Is 
there  any  chemical  action  ?  Place  the  mixture  on  a  brick 
or  piece  of  earthenware,  and  direct  the  flame  of  the 
Bunsen  burner  upon  it  until  reaction  begins.  Then  re- 
move the  flame.  What  evidence  is  there  of  chemical 
action  ?  Is  the  reaction  exothermic  or  endothermic  ? 
What  purpose  was  served  by  the  heat  that  was  first 
applied  ? 


12  LABORATORY  MANUAL  IN  CHEMISTRY 

EXP.  5.    WHAT  IS   FLAME  ? 

Materials.  Ether.  Kerosene.  Paraffin  or  tallow  can- 
dle. Sawdust. 

Apparatus  as  shown  in  Fig.  6.  Test  tubes,  burner,  and 
ring  stand. 

Procedure,  (a)  Recall  that  coal  gas,  illuminating  gas 
and  all  other  gases  you  know  of  burn  with  a  flame  (if 
they  burn  at  all). 

(5)  Put  3  ccm.  of  ether  (CAUTION  :  Do  not  bring  the 
bottle  of  ether  near  a  flame!)  in  a  test  tube  and  smell  of 
it.  Can  you  detect  it  by  its  odor  ?  Is  sufficient  ether 
vaporizing  to  burn  when  the  mouth  of  the  test  tube  is 
brought  to  a  flame  ?  Warm  the  test  tube  gently  and  see 
how  it  affects  the  size  of  the  flame.  Explain. 

(<?)  Put  5  ccm.  of  kerosene  in  a  test  tube  and  bring  it  to 
aflame.  Does  it  burn?  Why?  Heat  it  to  boiling  and 
bring  to  a  flame.  What  is  burning,  the  liquid  or  the 
gaseous  kerosene  ?  Does  the  flame  resemble  the  flame  of 
an  oil  lamp  ? 

(d)  Put  a  piece  of  a  paraffin  or  tallow  candle  in  a  test 
tube  and  bring  to  a  flame.  Does  it  burn  ?  Why  ?  Heat 
the  paraffin  or  tallow  until  it  begins  to 
bubble  or  smoke  and  then  bring  to  a 
flame.  Does  it  burn  ?  Is  it  a  solid,  a 
liquid  or  a  gas  that  burns  at  the  mouth 
of  the  test  tube  ? 

(e)  Set  up  the  apparatus  as  shown 
in  Fig.  6  and  support  on  a  ring  stand 
so   that   the    side-neck   test   tube    dips 
FlG<  6l  into  a  beaker  of  cold  water.      Fill  test 

tube  one  quarter  full  of  sawdust  or  pieces  of  wood  and 
heat  as  long  as  any  change  takes  place.  Note  the  con- 
densation of  liquid  in  the  side-neck  test  tube,  and  see  if 


EXPERIMENTS 


13 


you  can  get  anything  to  burn  at  the  exit  tube.  What  is 
it  that  burns  there  ?  Where  did  it  come  from  and  how 
was  it  produced  ?  Does  it  resemble  the  flame  of  burning 
wood  ?  Examine  the  material  left  in  the  test  tube. 
What  is  it  ?  How  can  you  make  charcoal  ?  What  else  is 
produced  in  the  same  process  ?  (The  liquid  in  the  side- 
neck  test  tube  is  mainly  water  mixed  with  a  little  acetic 
acid,  wood  alcohol  and  tar.) 

From  your  experiments,  what  is  flame  ?  What  sub- 
stances burn  with  a  flame  ?  Would  you  expect  charcoal 
to  burn  with  a  flame  ?  Why  ? 


EXP.  6.     WHEN  A  SUBSTANCE    BURNS,   IS  THERE  ANY 
CHANGE  IN  WEIGHT? 

Instructor's  Experiment 

Materials.  Small  candles.  Metallic  tin.  Clear  lime 
water.  Sticks  of  sodium  or  potassium  hydroxid  or  pieces 
of  quicklime. 

Apparatus.  A  fruit  jar  or  wide-mouthed  bottle  covered 
by  a  glass  plate.  A  wire  about  30  cm.  long.  A  porce- 
lain crucible  supported 
on  a  pipe-stem  triangle. 
Large  balance,  lamp  chim- 
ney filled  with  pieces  of 
sodium  or  potassium  hy- 
droxid or  lumps  of  quick- 
lime as  shown  in  Fig.  7. 
If  a  suitable  large  balance 
is  not  available,  use  Har- 
vard trip  scale,  placing 
the  chimney  on  a  piece  of  FlG  7 

wire  gauze  supported  on 

a  circle  of  gauze  as  shown  in  Fig.  8 ;  or  improvise  large 
balance  with  meter  rod,  etc. 


14          LABORATORY  MANUAL  IN  CHEMISTRY 

Procedure,     (a)  Set  a  candle  upright  on  the  pan  of  a 
balance  and  counterpoise  it  exactly  with  weights.     Light 
the  candle.     As  it  burns,  is  there  an  apparent 
gain  or  loss  in  weight  ? 

(£>)  In  a  shallow  crucible  without  a  cover  place 
5-10  g.  of  metallic  tin  and  weigh  on  a  balance 
that  is  sensitive  to  1  eg.     Support  the  crucible  in 
the  triangle  and  heat,  gently  at  first.     After  half 
an  hour  allow  the  crucible  and  contents  to  cool 
and  weigh  again.     Is   there   a   gain  or  loss  of 
weight  ?     What   does    the   change   of    weight   indicate  ? 
From  what  source  must  the  new  material  have  come  ? 

NOTE.  The  metal  has  been  heated  in  air  exactly  as  the  candle 
was.  At  high  temperatures  such  metals  burn  with(  a  flame.  The 
products  formed  are  the  ashes  of  these  metals,  similar  to  the  products 
of  ordinary  combustion.  In  the  case  of  metals  the  ash  weighs  more 
than  the  original  substance.  Wood  and  coal  leave  some  ash.  Illu- 
minating gas,  petroleum  and  a  candle  apparently  burn  to  nothing 
and  form  no  ash.  Does  combustion  of  a  metal  differ  from  combus- 
tion of  a  candle,  or  may  it  be  that  the  ash  of  a  candle  is  gaseous  and 
so  escapes  notice?  To  test  this  point,  perform  the  following  ex- 
periment. 

(<?)  Add  50  ccm.  of  clear  lime  water  to  a  jar  of  air,  put 
on  the  glass  cover,  and  shake.  Does  the  air  produce  any 
marked  change  in  the  lime  water  ? 

Without  removing  the  lime  water,  lower  a  lighted 
candle  into  the  jar  by  means  of  a  wire  wound  around  one 
end,  and  cover  the  jar  with  the  piece  of  glass.  In  a  short 
time  what  happens  to  the  candle  flame  ?  To  be  sure  that 
the  candle  flame  has  not  been  accidentally  extinguished, 
take  out  the  candle,  relight  it  and  again  lower  it  into  the 
jar.  What  effect  does  the  burning  of  a  candle  have  on 
the  surrounding  air  ? 

Remove  the  candle  and  shake  the  lime  water  in  the  jar. 
What  change  do  you  notice?  Does  air  cause. this  change? 


EXPERIMENTS  15 

Are  the  products  of  combustion,  i.e.  the  ash  from  a  can- 
dle, solid,  liquid  or  gaseous  ? 

(d)  Potassium  hydroxid  or  quicklime  will  unite  with 
the  products  of  combustion  of  a  candle,  as  the  following 
experiment  shows.  To  see  whether  the  ash  from  a  candle 
weighs  more  than  the  candle,  use  the  apparatus  shown  in 
Fig.  7  or  Fig.  8.  After  making  sure  that  the  apparatus  is 
properly  balanced  and  responds  readily  to  a  slight  change 
of  weight  on  either  side,  light  the  candle.  As  it  burns, 
notice  the  change  in  weight  on  the  side  where  the  candle 
is  burning.  Is  there  a  gain  or  a  loss  in  weight?  Does  the 
candle  weigh  more  or  less  than  its  ash  ? 

Every  substance  has  been  found  to  gain  in  weight  when 
burned.  From  what  source  must  the  extra  matter  come? 


EXP.  7.  IS  THE  TOTAL  WEIGHT  OF  MATTER  AFTER  A 
CHANGE  THE  SAME  AS  THE  TOTAL  WEIGHT  OF  MAT- 
TER BEFORE  THE  CHANGE? 

Instructor's  Experiment 

Materials.  Potassium  iodid.  Mercuric  chlorid.  Phos- 
phorus.* 

Apparatus.  Porcelain  crucible.  Balance.  Magnifying 
glass  or  lens.  Two  clean  beakers  of  about  150  ccm. 
capacity.  Stirring  rods.  Flask  or  bottle  whose  capacity 
is  a  liter  or  more,  fitted  with  a  one-hole  rubber  stopper. 

*  Phosphorus  is  very  inflammable  ;  hence  special  precautions  are  neces- 
sary in  handling  it.  It  comes  into  the  laboratory  in  the  form  of  sticks, 
and  is  kept  under  water  to  prevent  its  catching  fire.  When  a  small  piece 
is  needed,  remove  a  stick  from  the  bottle,  put  it  in  a  shallow  dish  con- 
taining sufficient  water  to  cover  the  phosphorus,  and  cut  it  with  a  knife. 
A  piece  may  be  removed  from  the  dish  by  means  of  the  fingers,  if  it  is 
thoroughly  wet.  If  it  must  be  dried  before  use,  lay  it  on  a  piece  of  filter 
paper  or  a  damp  towel,  turn  it  over  a  few  times,  handling  it  with  forceps. 
If  through  any  accident  a  phosphorus  burn  is  inflicted  on  the  skin,  wash 
the  wound  well  and  cover  it  with  a  mixture  of  baking  soda  and  oil. 


16          LABORATORY  MANUAL   IN  CHEMISTRY 

Through  the  stopper  passes  a  combustion  spoon,*  so  that 
when  the  stopper  is  inserted  the  bowl  of  the  spoon  is 
below  the  center  of  the  space  inside  the  bottle.  If  the 
handle  of  the  combustion  spoon  does  not  fit  tightly  into 
the  stopper  when  it  is  inserted  into  the  bottle,  fasten  it 
with  sealing  wax.  Large  balance. 

Procedure,  (a)  Dry  a  piece  of  phosphorus  the  size  of 
a  small  pea,  pick  it  up  with  forceps  and  put  it  into  a 
crucible.  Set  the  phosphorus  on  fire  and  note  the  result. 

Dry  another  piece  of  phosphorus,  place  it  at  once  in  the 
combustion  spoon  and  introduce  the  latter  into  the  flask, 
fitting  the  stopper  tightly  so  that  the  whole  is  air-tight. 
Without  delay  counterbalance  the  flask  and  its  contents 
accurately. 

Ignite  the  phosphorus  in  the  flask  by  focusing  the  rays 
of  the  sun  on  it  by  means  of  a  lens. 

When  the  burning  is  over  and  the  flask  is  cool,  place 
it  upon  the  balance  again.  Explain  why  you  notice  no 
change  in  weight. 

How  do  you  account  for  the  change  in  weight  when  a 
candle  burns  —  first,  ordinarily  ;  secondly,  under  the  lamp 
chimney  containing  potassium  hydroxid  ?  If  the  candle 
were  burned  inside  of  a  sealed  flask,  would  there  be  gain 
or  loss  of  weight  ?  Why  ? 

(5)  Into  each  of  two  clean  beakers  put  50  com.  of  water. 
In  one  dissolve  3  g.  of  potassium  iodid  and  in  the  other  1  g. 
of  mercuric  chlorid,  stirring  until  the  crystals  have  dis- 
appeared. Then  place  the  beakers  with  their  contents  side 
by  side  on  one  pan  of  the  balance  and  counterpoise  them. 

Without  spilling  a  drop,  pour  one  half  of  the  potassium 

*  If  a  combustion  spoon  is  not  at  hand,  a  substitute  may  be  made  by 
wrapping  one  end  of  a  piece  of  wire  about  a  short  piece  of  electric  light 
carbon  or  chalk.  Make  a  shallow  depression  in  the  end  of  the  carbon  01 
chalk. 


EXPERIMENTS  17 

iodid  solution  into  the  other,  and  place  the  beakers  again     I 
side  by  side  on  the  balance  pan.     Do  you  judge  that  a  chem-   j 
ical  change  has  taken  place  ?     Why  ?     Is  it  accompanied  / 
by  a  change  in  the  total  weight  of  reacting  substances  ? 

Without  spilling  a  drop,  pour  the  rest  of  the  potassium 
iodid  solution  into  the  second  beaker.  Would  you  say 
that  a  chemical  reaction  had  taken  place  ?  Why  ?  Do 
you  note  any  change  in  weight  ? 

These  reactions  are  typical  examples.  State  the  prin- 
ciple which  they  illustrate. 

EXP.  8.     THE  GAS  THAT  MAKES   A  FIRE  BURN 

Materials.     Mercuric  oxid.     A  wooden  splint. 
Apparatus.     A  test  tube  of  hard  glass. 

NOTE.  Mercury  heated  in  a  measured  volume  of  air  gains  in 
weight  and  burns  slowly  to  a  red  ash  called  mercuric  oxid.  When 
this  process  has  been  completed  about  one  fifth  of  the  air  has  been 
absorbed  and  the  remaining  four  fifths  will  not  support  combustion, 
for  the  mercury  has  taken  out  of  the  air  all  of  the  gas  that  makes 
mercury  or  other  substances  burn. 

Procedure.  By  means  of  a  slip  of  paper  neatly  insert 
about  2  g.  of  mercuric  oxid  into  the  end  of  a  hard  glass 
test  tube  and  heat,  gently  at  first.  Does  the  change  in 
color  indicate  a  3hemical  or  a  physical  change  ?  Allow 
the  tube  'to  cool  and  see  if  you  can  get  an  answer  to  this 
question.  Heat  the  tube  strongly  and  from  time  to  time 
insert  into  the  mouth  of  the  test  tube  a  glowing  spark  on 
the  end  of  a  match  or  a  splint  of  wood.  What  happens  ? 
What  is  the  gas  ? 

When  the  red  powder  is  entirely  decomposed,  allow  the 

tube  to  cool.     Then  hold  it  in  an  inverted  position  and  tap 

it  on  a  sheet  of  paper  laid  on  the  table  top.     In  addition 

to  oxygen,  what  substance  has  been  formed  in  this  reaction  ? 

,  This  experiment  was  first  performed  by  Priestley  in  1774. 


18          LABORATORY  MANUAL  IN   CHEMISTRY 

EXP.  9.    HOW  MAY  THE   SPEED  OF  REACTIONS  BE 
INCREASED  ? 

Materials.  Potassium  chlorate.  Powdered  manganese 
dioxid. 

Apparatus.     Two  test  tubes. 

Procedure,     (#)  By  increase  of  temperature. 

In  a  test  tube  heat  about  5  g.  of  potassium  chlorate  in 
the  flame  of  the  burner,  cautiously  at  first  until  the  potas- 
sium chlorate  has  melted.  Notice  that  though  minute 
bubbles  of  gas  are  evolved  the  total  amount  is  insignificant. 
Then  heat  the  contents  of  the  tube  to  a  much  higher  tem- 
perature and  note  the  increase  in  the  speed  of  the  reaction 
with  the  increase  in  the  temperature.  Test  the  gas  with 
a  spark.  What  is  it  ? 

(5)  By  catalytic  agents. 

Heat  a  second  portion  of  potassium  chlorate  in  a  test 
tube  as  before,  until  it  has  become  thoroughly  liquid. 
Remove  the  test  tube  from  the  flame,  and,  while  its  con- 
tents are  still  liquid,  drop  in  a  small  pinch  of  powdered 
manganese  dioxid,  directing  the  mouth  of  the  test  tube 
away  from  the  face.  What  happens  ?  Test  the  gas 
liberated  with  a  spark.  What  is  it  ? 

Is  the  difference  in  the  rate  at  which  the  gas  is  produced 
due  to  the  liberation  of  oxygen  from  manganese  dioxid  ? 
To  test  this  point  the  contents  of  the  test  tube  may  be 
cooled  and  then  boiled  out  with  water.  All  but  the  black 
manganese  dioxid  will  dissolve  and  may  be  poured  off 
from  the  residue.  If  the  manipulation  is  carefully  per- 
formed, the  manganese  dioxid  will  be  found  in  exactly 
the  same  condition  and  quantity  in  which  it  was  intro- 
duced. Why,  then,  is  it  well  to  mix  manganese  dioxid 
with  the  potassium  chlorate  in  preparing  oxygen  ? 

Set  up  the  apparatus  for  the  next  experiment. 


EXPERIMENTS 


19 


EXP.  10.     PREPARATION  AND  PROPERTIES   OF  OXYGEN 

Materials.  A  mixture  of  30  g.  of  potassium  chlorate 
and  15  g.  of  finely  powdered  manganese  dioxid.*  The 
materials  need  not  be  ground  together.  Small  pieces  of 
charcoal,  sulfur  and  phosphorus.  Iron  picture  wire. 

Apparatus  as  shown  in  Fig.  9.  Five  or  6  pint  fruit  jars 
or  wide-mouth  bottles.  Combustion  spoon. 

Procedure,     (a)  Preparation. 

Fill  the  bottles  full  of  water,  cover  each  with  a  glass 
plate  and  invert  them  in  the  pneumatic  trough,  taking 
care  that  no  air  is  al- 
lowed to  enter.  Put 
the  potassium  chlorate 
and  manganese  dioxid 
mixture  into  the  test 
tube  until  it  is  about 
one  third  full  and  ar- 
range the  apparatus  as 
shown  in  Fig.  9.  Heat 
gently  at  first,  prevent- 
ing moisture  from  con- 
densing and  running  down  upon  the  hot  glass  by  occasion- 
ally waving  the  flame  up  the  test  tube.  The  first  bubbles 
of  gas  driven  out  of  the  apparatus  are  air ;  they  may  be 
allowed  to  escape. 

When  gas  is  being  liberated  in  a  steady  stream  of 
bubbles,  place  one  of  the  bottles  full  of  water  on  the  small 
pan  in  the  pneumatic  trough  over  the  hole  from  which  the 
bubbles  are  rising,  being  careful  to  keep  the  mouth  of  the 

*  Manganese  dioxid  is  sometimes  mixed  with  carbonaceous  matter,  and 
violent  explosions  have  resulted  from  using  it  in  this  condition.  To  test 
the  purity  of  the  substance  used,  heat  about  1  g.  of  the  above  mixture  in 
a  test  tube.  If  chemical  action  goes  on  quietly,  proceed  with  the  work. 


FIG.  9. 


20          LABORATORY  MANUAL   IN   CHEMISTRY 

bottle  always  under  water  so  that  no  air  enters.  Fill  five 
or  six  jars  or  bottles  in  a  similar  way.  Before  removing 
from  the  water,  close  the  mouth  of  each  bottle  with  glass 
plate  or  screw  on  the  cover  of  the  jar.  Heat  the  test  tube 
only  sufficiently  to  produce  a  steady  flow  of  gas,  removing 
the  flame  for  a  moment  if  the  gas  is  liberated  too  rapidly. 
When  the  jars  are  full,  remove  the  delivery  tube  from 
the  water  to  prevent  sucking  back  and  breaking  the  test 
tube. 

It  is  a  good  plan  to  keep  the  jars  of  gas  wrong  side  up 
after  closing  them,  as  the  small  amount  of  water  they 
usually  contain  will  stop  any  leaks  around  the  covers. 

After  it  has  cooled,  water  may  be  added  to  the  test  tube 
to  clean  it. 

(6)  Physical  properties. 

Note  whether  oxygen  has  any  color,  taste  or  odor. 
Remembering  that  air  contains  oxygen,  does  this  agree 
with  your  everyday  experience  ? 

(c)    Chemical  properties. 

1.  Action  on  charcoal.     Place  a  piece  of  charcoal  in  a 
combustion  spoon  and  heat  it  in  the  flame  of  the  burner 
until  it  glows.     Remove  it  from  the  flame.     Does  char- 
coal burn  readily  in  the  air  ? 

Again  heat  a  piece  of  charcoal  and  insert  it  still  glow- 
ing into  a  bottle  of  oxygen.  Compare  the  burning  of 
charcoal  in  air  and  in  oxygen. 

2.  Action   on    sulfur.     (Hood.)      Repeat  (1)  with    a 
fresh  bottle  of  oxygen,  using  sulfur  instead  of  charcoal. 
Compare   the   burning   of   sulfur  in  air  and  in  oxygen. 
Cautiously  ascertain  by  the  odors  whether  the  two  prod- 
ucts are  the  same.     Is  the  chemical  action  endothermic 
or  exothermic  ? 


EXPERIMENTS  21 

3.  Action  on  phosphorus.     (Hood.)     Place  a  small  bit 
of  yellow  phosphorus  in  a  combustion  spoon,  light  it  and 
notice  how  it  burns  in  air. 

After  the  spoon  has  cooled,  and  not  before,  put  another 
piece  of  dry  phosphorus  in  it,  ignite  it  and  insert  in  a 
bottle  of  oxygen.  Do  not  let  the  burning  phosphorus 
get  against  the  sides  of  the  bottle.  Compare  with  phos- 
phorus burning  in  air. 

4.  Action   on   iron.     Place   sand   in  a   jar  of   oxygen 
sufficient  to  form  an  even  layer  over  the  bottom.     Heat 
the  end  of  a  piece  of  iron  picture  wire  about  30  cm.  long 
and  dip  it  into  powdered  sulfur.     Light  the  sulfur  and 
note  whether  the  iron  will  take  fire  in  air.     Repeat  and 
insert   the  lighted  end  into  the  bottle  of  oxygen.     The 
heat  from  the  burning  sulfur  causes  the  iron  to  catch  fire. 
(Repeat  if   not   successful  at  the   first  trial.)     Describe 
what  happened. 

What  can  you  say  of  the  chemical  activity  of  oxygen 
at  ordinary  and  at  more  elevated  temperatures  ? 

EXP.  11.    OXYGEN  CONSUMED  DURING  COMBUSTION 

Instructor's  Experiment 

Materials.  Potassium  chlorate.  Manganese  dioxid. 
About  1  m.  of  iron  picture  wire.  Powdered  iron.  Yel- 
low phosphorus. 

Apparatus.  A  stoppered  bell  jar  or  a  two-liter  bottle 
cut  off  *  near  the  bottom,  or  simply  with  a  hole  broken 
in  the  bottom.  Two  one-hole  stoppers  to  fit  the  bottle. 
Two  pieces  of  glass  tubing  fitting  the  stoppers,  about  20 
cm.  long.  A  short  piece  of  rubber  tubing.  A  pinchcock. 
An  oxygen  generator.  Two  closed  tubes,  preferably  gradu- 
ated, 30  cm.  or  more  in  length  and  about  2  cm.  in  diame- 

*  To  cut  a  glass  bottle,  see  p.  28. 


22 


LABORATORY  MANUAL  IN  CHEMISTRY 


ter.  Stout  wire  about  half  as  long  as  the  tubes.  Two 
tall  beakers  or  cylinders.  Ring  stand  and  large  clamp. 
Tank  or  pail  for  holding  water. 

Procedure,     (a)  Rapid  combustion. 

Slip  one  piece  of  glass  tubing  through  one  of  the  stop- 
pers, put  the  stopper  tightly  in  the  bottle  and  connect 
the  rubber  tube  to  the  end  of  the  glass  tube  projecting 
from  the  stopper.  Set  the  bottle  in  a  tank  or  pail  of 
water  and  fill  it  by  sucking  on  the  rubber  tube ;  then 
close  the  rubber  tube  with  a  pinchcock.  Support  the 
bottle  by  a  clamp  and  ring  stand  and  fill  it  with  oxygen. 
Raise  or  lower  the  bottle  to  make  the  water  level  the 
same  inside  as  outside,  and  mark  the  level  with  chalk  or 
an  elastic. 

Wrap  the  picture  wire  around  a  pencil  in  a  close  spiral. 
Remove  the  pencil,  and  tip  the  end  of  the  wire  with  sul- 
fur as  in  Exp.  10.  Fuse  a  copper  wire 
loop  into  one  end  of  the  second  piece 
of  glass  tubing,  seal  the  other  end, 
and  slip  it  through  the  hole  in  the 
second  rubber  stopper.  Hang  the 
coil  of  wire  from  the  loop. 

Light  the  sulfur,  then  quickly  re- 
moving the  first  stopper  insert  the 
other  stopper  tightly  so  that  the  pic- 
ture cord  may  burn  in  oxygen,  as  shown 
in  Fig.  10.  Slip  the  glass  tube  up  or 
down  through  the  stopper  and  lower  the  bottle  in  the 
water  if  necessary  to  prevent  ingress  of  air. 

The  picture  wire  is  now  burning  in  a  closed  space  filled 
with  oxygen.  As  the  combustion  progresses,  what 
change  is  seen  in  the  water  level  inside  the  bottle  ? 
What  must  have  become  of  the  oxygen  ?  What  must  be 


FIG.  10. 


EXPERIMENTS  23 

the  composition  of  the  black  substance  at  the  bottom  of 
the  tank  ? 

(£>)    Slow  combustion. 

1.  Of  iron.     Fill    one    of   the    tubes    with  water  and 
invert  it  in  a   dish  of   water.     Then   fill   the  tube  with 
oxygen.     Close  the  end  of  the  tube  with  the  thumb  and 
remove  from  the  water.      Carefully  remove  the  thumb  for 
a   moment   and    introduce    5-10   g.    of    powdered    iron. 
Cover  with  the  thumb  and  shake  the  tube  until  the  iron 
distributes  itself  over  the  inside  of  the  tube.     Then  in- 
vert in  a  tall  beaker  of  water  and  stand  aside  for  a  day 
or  two.     Explain  what  happens.     Is  there  any  significant 
difference   between   this   reaction    and   that   in   the   last 
experiment  ? 

2.  Of    phosphorus.       Keeping   the    phosphorus   under 
water,  impale  a  piece  about  the  size  of  a  pea  on  the  end 
of  the  wire.     Place  the  other  end  of  the  wire  in  a  beaker 
of  water  and  slip  over  the  phosphorus  the  closed  tube,  so 
arranging  the  quantity  of  water  in  the  beaker  that  the 
phosphorus  shall  be  out  of  water  but  inclosed  in  the  tube 
full  of  air  over  water.     Stand  aside  for  three  or  four  days 
until   action    ceases.     Explain  what   happens.     What   is 
the  difference  between  this  experiment  and  that  with  the 
iron? 

This  reaction  offers  a  method  for  determining  the  pro- 
portion of  oxygen  in  air.  When  the  water  ceases  to  rise 
inside  the  tube,  showing  that  the  reaction  is  complete, 
make  the  level  of  the  water  inside  and  outside  the  tube 
the  same,  either  by  raising  the  tube  or  by  adding  water 
to  the  beaker.  Then  ascertain  the  proportion  of  the  gas 
absorbed.  This  is  the  proportion  of  oxygen  in  the  atmos- 
phere. What  do  you  find  it  to  be  ? 


24          LABORATORY  MANUAL  IN   CHEMISTRY 

EXP.  12.    HEAT  EVOLVED  DURING  SLOW  OXIDATION 
LEADS   TO   SPONTANEOUS  COMBUSTION 

Instructor's  Experiment 

Materials.  Yellow  phosphorus.  Carbon  disulfid. 
Cotton. 

Procedure.  Dry  a  small  piece  of  phosphorus  and  lay  it 
on  a  glass  plate.  .  Notice  how  it  smokes  after  a  few  seconds. 
How  do  you  explain  this  action  ? 

Dissolve  a  piece  of  dried  phosphorus  as  large  as  a  pea  in 
about  5  com.  of  carbon  disulfid  in  a  test  tube.  By  the 
aid  of  pincers  or  a  piece  of  wire  (CAUTION  :  Do  not 
handle  with  the  fingers !)  dip  a  little  cotton  in  the  solu- 
tion of  phosphorus  and  spread  it  out  on  the  ring  of  an  iron 
stand.  The  carbon  disulfid  evaporates  quickly,  leaving 
the  phosphorus  in  finely  divided  condition,  so  that  a  large 
surface  is  exposed  to  the  action  of  the  air.  Note  what 
happens  presently.  How  do  you  explain  it? 

EXP.  13.    KINDLING  TEMPERATURE 

Materials.  Yellow  phosphorus.  Sulfur.  Paraffin. 
Sulfur  matches.  Parlor  matches. 

Apparatus.  A  small  pan,  such  as  is  used  for  a  sand 
bath,  or  piece  of  sheet  iron.  Gauze.  Tripod  or  ringstand. 

Procedure.     (#)  A  study  of  a  match. 

At  equal  distances  from  the  center  of  the  pan  or  piece  of 
sheet  iron  and  as  far  as  possible  from  each  other,  place  a 
small  piece  of  dried  phosphorus,  of  sulfur,  of  paraffin, 
and  a  match  from  which  the  head  has  been  removed.  Set 
the  pan  on  a  tripod,  and  under  its  center  place  a  burner. 
Presumably  the  substances  are  heated  equally  rapidly. 
Notice  the  order  in  which  the  substances  catch  fire.  That 
which  takes  fire  first  has  the  lowest  kindling  temperature. 


EXPERIMENTS  25 

Examine  a  sulfur  match.  Do  you  get  any  indication  of 
the  substances  composing  it  ?  (Match  heads  formerly 
contained  phosphorus,  but  because  of  its  poisonous  prop- 
erties, phosphorus  sulfid  is  now  used,  its  kindling  temper- 
ature being  about  the  same  as  for  phosphorus.) 

Rub  a  similar  match  against  a  slightly  roughened  sur- 
face. What  substance  first  catches  fire?  Whence  does  it 
derive  the  heat  necessary  to  raise  it  to  its  kindling  tem- 
perature? Which  substance  burns  next?  Whence  does 
it  derive  the  heat  necessary  to  raise  it  to  its  kindling  tem- 
perature? Which  substance  burns  last? 

Repeat  the  work  of  the  last  two  paragraphs,  using  parlor 
matches.  What  difference  in  the  composition  of  parlor 
and  sulfur  matches  is  evidenced  ? 

What  would  be  the  effect  if  a  match  were  tipped  with 
sulfur  alone?  (Try  to  ignite  a  piece  of  sulfur  by  friction.) 

If  wood  had  a  lower  kindling  temperature,  which  part 
of  a  match  could  be  left  out  ? 

In  burning  iron  in  oxygen,  why  was  the  picture  cord 
tipped  with  sulfur? 

(b)   The  kindling  temperature  of  gases. 

Light  a  Bunsen  burner,  and  bring  down  over  the  flame  a 
piece  of  wire  gauze.  Why  does  the  flame  not  burn  above 
the  gauze  ?  Is  there  unburned  gas  above  the  gauze  ?  To 
answer  this  question  hold  a  lighted  match  above  the  gauze 
and  explain  the  result.  What  cools  the  gas  above  the 
gauze  below  its  kindling  temperature  ? 

Remove  the  gauze  from  the  flame  for  a  moment  and, 
while  it  is  still  hot,  bring  it  down  into  the  flame  again. 
Why  does  the  gas  above  the  gauze  now  catch  fire  ? 

Turn  off  the  gas  in  the  burner.  Then  turn  it  on  again 
but  do  not  light  it,  and  bring  down  a  piece  of  cold  wire 
gauze  to  a  distance  of  about  5  cm.  above  the  top  of  the 


26    LABORATORY  MANUAL  IN  CHEMISTRY 

burner.  Bring  a  lighted  match  above  the  gauze.  Under 
proper  conditions  the  gas  burns  above  but  not  below  the 
gauze.  Why  not? 

NOTE.  The  safety  lamp,  invented  by  Sir  Humphry  Davy  and 
used  by  miners,  depends  on  the  principle  illustrated  in  the  preceding 
experiments.  It  consists  of  a  small  lamp  surrounded  by  fine  wire 
gauze.  When  brought  into  a  mine  where  combustible  gas  is  present, 
the  gas  passes  readily  through  the  wire  gauze  and  burns  brightly  on 
the  inside.  The  gauze  conducts  the  heat  of  the  flame  away,  and  pre- 
vents the  gas  outside  the  gauze  from  becoming  heated  to  its  kindling 
temperature.  Thus  the  miner  is  warned  that  a  dangerous  gas  is 
present. 

EXP.  14.    DIFFUSION 

Instructor's  Experiment 

Materials.  B-romin.*  Cupric  chlorid.  Ammonia  water 
(ammonium  hydroxid).  Alcohol.  Alcoholic  solution  of 
phenolphthalein.  Dilute  sodium  hydroxid  solution. 

Apparatus.  Fruit  jar,  or  wide-mouth  bottle,  covered 
with  glass  plate.  A  thistle  tube.  Two  cylinders  cov- 
ered with  glass  plates  or  two  large  test  tubes  fitted  with 
corks.  A  separating  funnel  or  a  pipette. 

Procedure,   (a)    G-ases. 

Through  the  thistle  tube  deposit  about  1  ccm.  of 
bromin  inside  on  the  bottom  of  a  fruit  jar.  Remove  the 
thistle  tube  and  cover  with  a  glass  plate.  Notice  how, 
as  the  bromin  vaporizes,  it  rises  through  the  air  until  it 
soon  fills  the  whole  jar.  Are  the  particles  of  which  gases 
are  composed  capable  of  moving  with  great  freedom  ? 

*  Avoid  inhaling  the  fumes  of  bromin,  as  it  attacks  the  nose  and 
throat.  The  antidote  is  to  inhale  alcohol  poured  on  a  handkerchief. 
Do  not  allow  liquid  bromin  to  touch  the  skin,  as  it  produces  severe 
burns.  If  it  does  get  on  the  skin,  wash  quickly  with  water  and  then 
with  a  dilute  solution  of  baking  soda. 


EXPERIMENTS  27 

(5)    Liquids. 

1.  Make  a  concentrated  solution  of  cupric  chlorid  in 
a  little  cold  water.     To  1  com.  of  the  solution  in  a  test 
tube  add  a  little  ammonia  water,,  and  notice  the  deep 
blue  color  produced  when  the  liquids  mix. 

By  means  of  a  thistle  tube  pour  the  cupric  chlorid 
solution  into  a  cylinder  or  large  test  tube  until  there  is 
a  layer  2-3  cm.  thick,  taking  care  not  to  spatter  the 
sides  of  the  cylinder.  On  the  cupric  chlorid  solution 
float  water.  To  float  one  liquid  on  another,  cut  a  thin 
section  from  the  top  of  a  large  cork,  the  thinner  the 
better.  Place  the  section  of  cork  on  the  heavier  liquid, 
and  deliver  the  lighter  liquid  slowly  upon  the  center 
of  the  cork,  using  a  separating  funnel  or  a  pipette. 
When  the  test  tube  is  about  three  fourths  full,  float  a 
layer  of  ammonia  water  on  the  top  of  the  others.  Remove 
the  section  of  cork  and  without  disturbing  the  layers  of  / 
liquid,  cover  or  cork  the  cylinder  and  set  it  where  it  canjf  |M « 
remain  quiet  for  several  days.  It  now  contains  cupric  chlo- 
rid and  ammonia  separated  by  a  considerable  layer  of  water. 

From  day  to  day  notice  the  rise  of  the  blue  copper 
chlorid  through  the  tube  until  it  meets  the  ammonia 
diffusing  down  through  the  water,  as  is  indicated  by  the 
deep  blue  color. 

2.  Try  the  effect  of  bringing  together  a  few  drops  of 
an    alcoholic    solution    of   phenolphthalein    and    a    little 
dilute  sodium  hydroxid  solution.     Then  repeat  the  work 
outlined    in    the    preceding    paragraphs,    placing    in    the 
bottom  of  the  cylinder  sodium  hydroxid  solution,  on  it 
floating  a  mixture   of   alcohol  and   water  in   equal  pro- 
portions  until   the   test   tube   is    nearly  full,  and    lastly 
1    com.    of    an    alcoholic    solution    of    phenolphthalein. 
Remove    the    section    of    cork,  close    the    test  tube,  and 
stand  aside  as  in  (1).     Explain  the  final  result. 


28 


LABORATORY  MANUAL  IN  CHEMISTRY 


Are  the  particles  of  which  liquids  are  composed 
capable  of  moving  with  considerable  freedom  ?  How 
does  this  freedom  compare  with  the  freedom  of  motion 
of  the  particles  of  gaseous  bodies  ? 

(c)  Diffusion  takes  place  with  solids  just  as  with  gases 
^nd  liquids,  only  much  more  slowly. 

In  a  previous  exercise  it  was  found  that  gases  and 
liquids  react  chemically  much  more  readily  than  solids. 
Suggest  an  explanation  of  this  fact. 


EXP.  15.    DECOMPOSITION  OF  WATER  BY  ELECTRICITY 

Instructor's  Experiment 

Materials.     Sugar.     Cone,  sulfuric  acid.     Sodium  hy- 

droxid.     Sodium  sulfate. 

Apparatus   as    shown    in    Fig.    11,   consisting    of   two 

graduated   test  tubes  or   measuring   glasses.     The   bowl 

may  be  made  by  cutting  a  bottle. 
To  do  this,  tie  a  string  wet  with 
kerosene  tight  about  the  bottle 
where  it  is  desired  to  cut  it. 
Set  fire  to  the  oil,  rotating  the 
bottle  slowly  as  the  oil  burns. 
As  soon  as  the  string  burns 
through,  plunge  the  bottle  in 
water. 

Fit  the  mouth  of  the  bottle 
with  a  solid  rubber  stopper. 
Drive  a  wire  nail  through  this 
stopper  in  two  places,  thus  mak- 
ing holes  through  which  the  wires 
leading  to  the  electrodes  may  pass. 
The  electrodes  consist  of  two  pieces  of  platinum  foil 


EXPERIMENTS  29 

about  2  cm.  long  and  1  cm.  wide,  each  welded  *  on  to  a 
platinum  wire  about  7  cm.  long.  If  these  wires  are 
pushed  through  the  holes  in  the  stopper,  it  will  close 
about  them  water-tight.  Bend  the  platinum  wires  into 
the  form  of  hooks  and  hang  into  them  similarly  hooked 
copper  wires  leading  to  the  battery.  When  the  bowl  is 
filled  with  solution,  the  circuit  is  complete. 

Procedure.     (&)  Non-electrolytes. 

1.  Remove  the  measuring  tubes  and  rinse,  the  whole 
apparatus  with  distilled  water.     Then  pour  distilled  water 
into  the  bowl  until  it  is  nearly  full.     Connect  the  elec- 
trodes with  a  battery  or  some  other  source  of  electricity 
and  attempt  to  pass  a  direct  current  through  the  water." 
Do  you  notice  any  indication  that  a  current  is  passing? 
Is  pure  water  an  electrolyte  or  a  non-electrolyte  ? 

2.  Dissolve  5  g.  qf  sugar  in  the  water  in  the  bowl. 
Does    the  current   now  flow  through   the   solution?     Is 
sugar  an  electrolyte  ? 

(6)  Electrolytes. 

1.  Empty  the  sugar  solution  from  the  bowl,  rinse  with 
distilled  water   and  refill,  adding  about  5  g.  of   sodium 
hydroxid  to  the  water  in  the  bowl  and  stirring  to  mix 
thoroughly.     What  difference  do  you  notice  ?     Is  sodium 
hydroxid  an  electrolyte  or  a  non-electrolyte  ? 

2.  Empty  the  contents  of  the  bowl,  rinse  with  distilled 
water  and  refill  as  before,  adding  sodium  sulfate  to  the 
water.     Describe  what  happens.     Is  sodium  sulfate   an 
electrolyte  or  a  non-electrolyte  ? 

*  To  weld  platinum,  lay  the  foil  on  a  piece  of  flat  iron,  hold  the  wire 
in  the  position  desired  and  heat  both  with  a  tine  flame  from  a  blowpipe. 
When  they  become  red-hot,  a  light  blow  with  a  hammer  will  produce 
a  firm  weld. 


30          LABORATORY  MANUAL  IN   CHEMISTRY 

3.  Empty,  rinse  and  refill  the  bowl  as  before,  adding 
to  the  water  about  10  ccm.  of  cone,  sulfuric  acid,  stirring 
well  as  before.  Is  the  acid  an  electrolyte  ? 

(c)  Electrolysis  of  water. 

Disconnect  the  wires  and  stop  the  current.  Fill  the 
graduated  test  tubes  or  measuring  glasses  with  solution 
from  the  bowl,  close  with  the  thumb,  and  invert  in  the 
bowl,  placing  one  test  tube  over  each  electrode.  See  to 
it  that  no  bubbles  of  air  have  gained  access  to  these  meas- 
uring tubes.  Start  the  current  again,  so  regulating  its 
strength  as  to  cause  a  steady  liberation  of  bubbles  without 
any  undue  heating  of  the  wires  or  the  solution.  Note  the 
rate  at  which  the  gases  are  liberated. 

When  a  sufficient  amount  of  the  gases  has  been  collected, 
break  the  circuit,  and  measure  the  amount  of  gas  in  each 
tube  to  the  nearest  cubic  centimeter,  first  adjusting  the 
tubes  so  that  the  water  level  is  right.  If  this  cannot  be 
satisfactorily  accomplished  in  the  bowl,  close  the  tubes 
with  the  thumb  and  remove  to  a  vessel  of  water  of  suffi- 
cient depth.  No  correction  for  pressure,  temperature  or 
moisture  is  necessary,  as  the  gases  are  under  the  same 
conditions  when  measured.  What  is  the  relation  between 
the  volumes  of  the  two  gases  ? 

Slip  the  thumb  over  the  mouth  of  the  tube  containing 
the  smaller  amount  of  gas,  remove  it  from  the  water,  turn 
it  mouth  up,  and  test  its  contents  with  a  glowing  spark. 
What  gas  does  it  contain  ? 

The  gas  in  the  second  tube  is  called  hydrogen.  In  a 
similar  way  remove  the  second  tube  from  the  solution,  and 
test  its  contents  with  a  lighted  match  or  other  flame. 
What  happens  ? 

In  each  of  the  above  instances  the  current  will  continue 
to  flow  through  the  solution  until  the  water  is  used  up 


EXPERIMENTS  31 

and  the  other  substance  is  left.  Furthermore,  by  evapo- 
rating any  of  the  three  solutions  mentioned  the  original 
substance,  sodium  hydroxid,  sodium  sulfate  or  sulfuric 
acid  may  be  recovered.  This  shows  that  the  catalytic 
agents  are  not  used  up  but  that  the  gases  come  from  the 
decomposition  of  the  water.  What  can  be  said,  then,  as 
to  the  composition  of  water? 

(c?)    Calculations  of  results. 

1.  Multiply  the  volume  of  oxygen  by  0.00143  g.,  the 
weight  of  1  com.  of  oxygen.     Multiply  the  volume  of  hy- 
drogen by  0.00009  g.,  the  weight  of  1  com.  of  hydrogen. 
Divide  the  weight  of  the  oxygen  by  the  weight  of   the 
hydrogen.     How  many  parts   by  weight  of   oxygen   are 
present  in  water   for  every  1  part  of   hydrogen  ?     How 
many  parts  by  weight  of  water  contain  1  part  by  weight 
of  hydrogen  ? 

2.  Add   the  weights  of   oxygen  and   hydrogen.     The 
sum  is  the  weight -of  the  water  decomposed.     The  weight 
of   1  ccm.  of  steam  is  0.0008  g.     Calculate  the  volume 
which  this  water  would  have  occupied  if,  instead  of  being 
decomposed,  it  had  been  converted  into  steam. 

3.  Fill  in  the  blanks  in  the  following  statements  : 

.By  weight,  1  part  of  hydrogen  unites  with  (  )  parts 
of  oxygen  to  give  (  )  parts  of  water. 

By  volume  (  )  parts  of  hydrogen  unite  with  1  part  of 
oxygen  to  give  (  )  parts  of  steam. 

EXP.  16.    DECOMPOSITION  OF  WATER  BY  METALS 

Instructor's  Experiment 

Materials.  Iron  filings,  tacks  or  nails.  Sodium. 
Potassium. 

Apparatus  as  shown  in  Fig.  12,  consisting  of  a  flask  for 


32 


LABORATORY  MANUAL  IN   CHEMISTRY 


generating  steam  connected  with  a  piece  of  iron  pipe 
about  50  cm.  long  and  2-3  cm.  in  diameter,  containing 
iron  filings  or  nails.  From  this  pipe  an  exit  tube  leads 
into  a  bottle,  as  shown  in  the  figure,  in  which  the  excess 
steam  condenses.  From  this  a  delivery  tube  dips  under 
the  surface  of  a  pneumatic  trough.  If  a  furnace  is  not 
available,  heat  the  tube  with  several  Bunsen  burners.  A 


FIG.  12. 

metallic  capsule  for  sodium  and  a  stiff  wire  for  a  holder 
(see  Suggestions  to  Teachers)*     Wide-mouth  bottle. 

Procedure,  (#)  Decomposition  of  water  by  iron.  First 
performed  by  Lavoisier  in  1783  with  a  gun  barrel,  furnish- 
ing the  first  proof  that  water  is  not  an  element. 

Heat  the  middle  of  the  iron  pipe  to  redness  and  pass 
in  steam  from  the  flask.  After  the  air  has  been  driven 
from  the  apparatus,  collect  some  of  the  gas  in  an  inverted 
bottle  filled  with  water.  When  the  bottle  is  full  cover 
with  a  glass  plate  and  remove  the  bottle  from  the  water. 
Keeping  the  bottle  inverted  bring  to  a  flame  and  remove 
cover.  Describe  what  happens. 

Is  the  gas  apparently  like  either  gas  formed  when 
water  is  decomposed  by  means  of  electricity  ? 


EXPERIMENTS  33 

The  gas  is  hydrogen,  its  odor  being  due  to  impurities. 
Iron  is  an  element.  Where  must  the  hydrogen  come 
from? 

Fill  a  bottle  half  full  of  hydrogen,  raise  from  the  water, 
thus  allowing  air  to  enter  and  mix  with  the  hydrogen. 
Bring  to  a  flame  and  note  result.  Bring  out  clearly  the 
effect  of  mixing  air  with  hydrogen. 

Iron  and  some  other  metals  decompose  water  at  high 
temperature ;  magnesium  at  boiling  temperature ;  others 
at  ordinary  temperature. 

(5)  By  sodium  or  potassium. 

1.  Throw  a  piece  of  sodium  about  the  size  of  a  small 
pea  on  a  dish  of  water,  holding  a  sheet  of  glass  between 
you  and  the  dish  to  prevent  spattering.     What  happens  ? 

2.  Throw   a   similar   piece   of   potassium   into   water. 
What  happens? 

The  action  with  potassium  is  similar  to  that  of  sodium 
except  for  the  flame.  Either  the  metal  burns  or  else  a 
gas  is  given  off  which  burns. 

3.  To  settle  this  point,  fill  a  capsule  with  sodium,  twist 
it  firmly  into  the  wire  holder.     Fill  a  bottle  with  water, 
cover  with  a  glass  plate  and  invert  in  a  pan  of   water, 
being  sure  that   no  air   gets  into  the   bottle.     Lean  the 
bottle  against  one  edge  of  the  pan  and  quickly  thrust  the 
capsule,  mouth   down,  under   the    mouth   of   the   bottle 
(see  Fig.  29).     Regulate  the  flow  of  gas  by  slightly  in- 
clining the   capsule   as  the  action  slackens.     If  careless 
handling  allows  the  sodium  to  escape  from  the  capsule, 
stand  back  until  all  action  ceases.     Describe  what  happens. 

When  action  is  complete,  cover  the  mouth  of  the  bot- 
tle with  a  glass  plate,  remove  from  water  and  stand 
bottle  upright.  Bring  a  flame  to  the  mouth  of  the  bottle 
and  remove  the  glass  cover.  What  happens  ? 


34          LABORATORY  MANUAL  IN  CHEMISTRY 

The  gas  is  hydrogen,  colored  yellow  by  sodium. 
Sodium  and  potassium  are  elements.  Where  does  the 
hydrogen  come  from  ? 

Dip  the  ringers  in  the  water  into  which  the  sodium  and 
potassium  were  thrown  and  note  the  effect.  This  is  due 
to  compounds  of  these  metals  dissolved  in  the  water  (see 
Exp.  34). 

EXP.  17.    THE  ACTION  OF  METALS  ON  ACIDS 

Materials.  Small  pieces  of  zinc,  magnesium,  copper, 
kV^ibm  and  of  iron,  such  as  coarse  filings  or  small  nails. 
Sulfuric,  hydrochloric  and  acetic  acids. 

Apparatus.     Test  tubes  and  an  evaporating  dish. 

Procedure,  (a)  Fill  a  test  tube  one  quarter  full  of  sul- 
furic  acid,  then  fill  to  the  top  with  water.  Close  the  tube 
with  the  thumb  and  invert  in  an  evaporating  dish  con- 
taining water.  Roll  about  7  cm.  of  magnesium  ribbon  into 
a  ball,  slip  it  under  the  mouth  of  the  test  tube  and  note 
action.  When  the  tube  is  full  of  gas,  close  with  the 
thumb  and  bring  to  a  flame.  What  happens  ? 

The  gas  is  hydrogen.  Magnesium  is  an  element. 
Where  must  the  hydrogen  have  come  from  ?  (See  if 
magnesium  acts  on  water  to  liberate  a  gas.) 

(5)  Without  attempting  to  collect  the  gas  as  in 
(a)  see  if  there  is  any  action  between  the  following  metals 
and  acids  by  adding  to  5  ccm.  of  acid  in  a  test  tube  a 
piece  of  the  metal.  Warm  the  acid  if  necessary  to  get 
action  but  do  not  heat  to  boiling.  State  whether  the 
action  is  slow,  medium  or  rapid  in  the  following  cases : 

Zinc  and  sulfuric  acid. 

Zinc  and  hydrochloric  acid. 

Zinc  and  acetic  acid. 

Iron  and  sulfuric  acid. 


EXPERIMENTS  35 

Tin  and  hydrochloric  acid. 

Magnesium  and  acetic  acid. 

Copper  and  sulfuric  acid. 

Copper  and  hydrochloric  acid. 

Many  metals  (not  all)  decompose  many  acids  (not  all) 
with  the  liberation  of  hydrogen. 

(Set  up  the  apparatus  for  the  next  experiment  so  that 
it  will  be  ready  at  the  beginning  of  the  period.) 

EXP.  18.    PREPARATION  AND  PROPERTIES  OF  HYDROGEN 

Materials.  Sulfuric  acid.  Granulated  zinc  or  small 
pieces  of  sheet  zinc.  Solutions  of  potassium  permanga- 
nate and  copper  sulfate.  Wooden  splints.  Cobalt  chlorid 
test  paper  (see  Exp.  26). 

Apparatus  as  shown  in  Fig.  13  consisting  of  a  bottle 
whose  capacity  is  about  300  ccm.  The  thistle  tube 
reaches  almost  to  the  bottom 
of  the  bottle.  A  piece  of  clay 
pipestem.  Two  250  ccm.  flasks 
closed  with  corks.  A  test  tube. 
4-6  fruit  jars  or  wide-mouth 
bottles. 

Procedure,     (#)  Preparation. 

Put  20-25   g.    of  granulated  FlG<  13' 

zinc  into  the  bottle,  insert  the  stopper  (fitted  with  the 
thistle  tube  and  delivery  tube  as  shown)  tightly,  and 
through  the  thistle  tube  pour  in  enough  sulfuric  acid  to 
cover  the  end  of  the  thistle  tube. 

If  the  action  is  slow,  add  a  little  copper  sulfate  solution 
and  shake  the  bottle.  What  is  the  effect  ?  The  copper 
sulfate  is  decomposed  by  the  zinc,  the  copper  being  de- 
posited on  the  zinc  as  is  shown  by  the  dark  coloration. 
The  copper  then  acts  as  a  catalytic  agent. 


36          LABORATORY  MANUAL  IN  CHEMISTRY 

CAUTION  :  The  hydrogen  liberated  is  at  first  mixed 
with  air.  A  hydrogen  and  air  mixture  is  explosive  ;  hence 
keep  all  flames  away  from  the  apparatus  at  this  stage  of 
the  work. 

To  ascertain  when  the  hydrogen  is  sufficiently  pure, 
collect  a  test  tube  of  the  gas  over  water,  cover  with  the 
thumb  and,  keeping  the  test  tube  inverted  remove  it  to  a 
flame.  If  a  whistling  noise  is  heard,  the  hydrogen  is  still 
mixed  with  air.  When  it  burns  with  only  a  quiet  puff  at 
the  beginning,  it  is  sufficiently  pure. 

Collect  six  bottles  of  hydrogen  gas,  after  sealing  allow- 
ing them  to  stand  inverted  until  used.  If  the  flow  of  gas 
slackens,  introduce  through  the  thistle  tube  additional 
acid.  Keep  the  apparatus  for  the  next  experiment. 

(5)  Properties. 

1.  Place  one  jar  of  hydrogen  mouth   upward  on   the 
table  and  another  mouth  downward.     Remove    the  seal 
from  second  jar  and  hold  it  mouth  downward  above  the 
table.      Then  remove  the    cover  from    the   upright  jar. 
After  about  a  minute  bring  both  jars  to  a  flame.     Do  you 
detect  hydrogen  in  both  bottles  ?     If  not,  from  which  one 
has  it  escaped  ?      How  did  it  escape  from  this  bottle  ? 
What   does   this   indicate  as  to   the  relative  weights  of 
hydrogen  and  air  ? 

2.  Note  whether  hydrogen  has  any  color,  taste  or  odor. 
If  impurities  give  to  the  gas  an   odor,  they  may  be  re- 
moved by  treating  with  a  dilute   solution  of   potassium 
permanganate   acidified  with    sulfuric    acid.       Slide    the 
cover  glass  partly  from  a  jar  of  hydrogen  and  quickly 
(Why  use  haste  ?)  introduce  the  permanganate  solution. 
Shake  the  covered  jar  for  a  few  minutes  and  then  test 
odor  again. 

3.  Remove  the  seal  from  a  jar  of  hydrogen  and,  hold- 


EXPERIMENTS  37 

ing  it  mouth  downward,  thrust  well  into  the  jar  a  lighted 
splinter  of  wood  and  hold  it  there  until  all  action  ceases 
(see  Fig.  14).     What  do  you 
observe  ? 

Does  hydrogen  support 
combustion  as  well  as  burn  ? 

4.  Slip  into  the  end  of  the 
rubber  tube  attached  to  the 
outlet  tube  of  the  generator  a 
piece  of  clay  pipestem  and 
light  the  escaping  hydrogen. 
Hold  in  the  flame  a  wire  or 

piece  of  glass  tubing.     Does  the  flame  seem  to  be  very 
hot? 

Hold  a  clean,  well-corked  flask  filled  with  cold  water 
20-30  cm.  above  the  hydrogen  flame.  What  happens  ? 

Blow  out  the  hydrogen  flame  and  hold  the  second  clean, 
well-corked  flask  filled  with  cold  water  in  the  hydrogen 
as  it  escapes  unburned.  What  happens  ? 

A  test  for  water  is  given  on  page  48.  Rub  off  the  de- 
posit on  the  first  flask  with  a  piece  of  cobalt  chlorid  paper, 
made  blue  by  warming.  What  happens  ?  What  was  the 
deposit  on  the  first  flask  ?  Explain  its  formation. 

(<?)  Another  product  of  the  reaction  remains  dissolved  in 
the  liquid  in  the  hydrogen  generator.  It  may  be  recovered 
as  follows  :  Allow  the  acid  to  stand  in  contact  with  zinc 
until  all  action  ceases,  then  pour  it  off  into  a  beaker. 
Allow  the  particles  of  copper  and  other  matter  to  settle, 
then  carefully  pour  off  the  clear  liquid  into  another  beaker 
or  evaporating  dish.  If  crystals  do  not  form  on  standing 
overnight,  evaporate  part  of  the  liquid  and  try  again. 
The  crystals  are  zinc  sulfate. 


38 


LABORATORY  MANUAL  IN  CHEMISTRY 


EXP.  19.    OXIDATION  AND  REDUCTION 

Materials.     Small  bits  of  copper  or  lead. 

Apparatus.  A  piece  of  hard  glass  tubing  about  30  cm. 
long  by  1  cni.  in  diameter  bent  nearly  at  a  right  angle,  as 
shown  in  Fig.  15.  A  hydrogen  generator  connected  to  a 
drying  tube  filled  with  granulated  calcium  chlorid  kept 
in  position  by  plugs  of  cotton  in  either  end  of  the  tube. 
Wire. 

Procedure,     (a)    Oxidation. 

Fill  .the  middle  of  the  hard  glass  tube  with  pieces  of 
copper  or  a  few  pieces  of  lead.  Support  this  tube  "on  a 
wire  gauze  placed  on  an  iron  ring,  keeping  the  short 
end  of  this  tube  nearly  vertical  by  means  of  a  piece  of 
wire  fastened  to  the  ring  stand.  Keep  the  vertical  tube 
heated  somewhat  so  as  to  cause  a  current  of  air  to  pass 
through  th.e  apparatus.  Heat  the  metal  in  the  tube,  gently 
at  first,  then  to  a  low  red  heat.  Notice  the  change  in  color 
of  the  copper  or  lead.  How  do  you  explain  this  action  ? 

Continue  the  heating  for  10-15  minutes,  then  allow  the 
apparatus  to  cool.  Complete  the  reactions : 


Copper  4-  oxygen 
Lead  +  oxygen 


(5)  Reduction. 


FIG.  15. 


While  the  tube  is 
cooling  start  the  hy- 
drogen  generator 
and  see  that  all  air 
has  been  driven  out. 
Then  connect  the 
drying  tube  of  the 
generator  to  the  tube 
containing  the  oxi- 


EXPERIMENTS  39 

dized  metal  as  shown  in  Fig.  15.  While  the  hydrogen  is 
passing  through  this  tube,  gently  heat  it  as  before,  allow- 
ing the  upright  tube  to  remain  cool.  Describe  and  explain 
what  takes  place. 

What  collects  in  the  cool  portion  of  the  exit  tube  ?  Test 
it  and  see  if  your  answer  is  correct. 

Copper  oxid  +  hydrogen  — > 
Lead  oxid  +  hydrogen  -> 

Consult  the  text,  page  61,  and  see  how -this  experiment 
might  be  made  of  use  in  determining  quantitatively  the 
composition  of  water. 

EXP.  20.    THE  NASCENT  STATE 

Materials.  200  ccm.  of  distilled  water,  to  which  is 
added  just  enough  potassium  permanganate  to  impart  a 
decided  color.  Cone,  sulfuric  acid. 

Apparatus.     Four  beakers.     A  hydrogen  generator. 

Procedure.  Divide  the  water  containing  potassium  per- 
manganate solution  into  four  portions. 

1.  To  one  portion  add  5  ccm.  of  cone,  sulfuric  acid. 

2.  Into  another  portion  drop  a  few  grams  of  zinc. 

3.  Into  a  third  portion  drop  a  similar  amount  of  zinc, 
and  then  add  5  ccm.  of  cone,  sulphuric  acid. 

4.  Through  the  last  portion  allow  hydrogen  from  the 
generator  to  bubble. 

After  about  20  minutes  compare  the  results  in  the  four 
solutions.  In  which  case  is  there  a  chemical  change  re- 
sulting in  the  bleaching  of  the  potassium  permanganate  ? 
Can  sulfuric  acid  alone  cause  the  bleaching  ?  Can  zinc 
alone  ?  What  do  they  produce  when  they  react  ?  Does 
ordinary  hydrogen  cause  the  bleaching?  In  what  condi- 
tion is  hydrogen  most  active  ? 


40          LABORATORY  MANUAL  IN  CHEMISTRY 

EXP.  21.    DECANTATION,  FILTRATION  AND  DISTILLATION 

Materials.  Filter  papers.  Sand.  Salt.  A  light  in- 
soluble powder,  such  as  precipitated  chalk  (calcium  car- 
bonate) or  magnesia  (magnesium  oxid).  Red  ink  or 
potassium  permanganate  solution. 

Apparatus.  Funnel,  ring  stand,  beakers  and  stirring 
rods.  Distillation  apparatus  as  shown  in  Fig.  18,  consist- 
ing of  a  condenser,  boiling  flask  of  about  a  half  liter 
capacity  fitted  to  it  and  a  receiving  flask  of  about  half 
this  capacity.  If  a  condenser  is  not  available,  a  long  piece 
of  glass  tubing,  a  meter  or  more  in  length,  will  serve  the 
purpose  if  the  boiling  is  sufficiently  slow  to  allow  the  air 
to  cool  and  condense  the  steam. 

Procedure,     (a)  Decantation. 

Stir  a  little  sand  into  a  beaker  half  full  of  water,  then 
allow  the  mixture  to  stand  for  a  few  minutes.  To  what 
extent  does  the  sand  settle  out  of  the  water  ?  See  how 
completely  you  can  separate  the  sand  by  carefully  pouring 
off  the  water.  This  process  of  pouring  off  is  called  de- 
cantation;  the  sand  is  typical  of  any  heavy  insoluble 
substance. 

Mix  about  50  g.  of  sand  with  10  g.  of  salt,  add  50  ccm. 
of  water,  stir  well,  then  allow  to  settle  and  see  how  com- 
pletely you  can  decant  into  a  beaker  the  liquid  without 
allowing  any  sand  to  be  poured  off.  Taste  and  measure 
the  liquid.  Where  is  the  salt  ?  Calculate  how  much  of 
the  salt  was  removed  from  the  sand  by  decanting  the 
liquid.  Add  50  ccm.  of  water  to  the  beaker  containing 
the  sand,  stir,  settle  and  decant  as  before.  Calculate  how 
much  salt  is  left  with  the  sand  after  the  second  decantation. 

Continue  the  process  until  the  taste  of  salt  is  no  longer 
perceptible.  How  many  decantations  were  necessary  to 


EXPERIMENTS 


41 


separate  the  salt  and  sand  ?  What  class  of  substances  can 
be  separated  from  what  other  class  of  substances  by  this 
method  ?  Suggest  practical  uses  of  the  process  of  de- 
cantation. 

(by   Filtration. 

To  50  ccm.  of  water  add  about  5  g.  of  salt  and  some 

precipitated  chalk  or  magnesia, 

stir  well  and  allow  to  settle  for 

a  few  moments.     Do  you  judge 

that  decantation  would  be  as  suc- 
cessful now  as  in  (#)  ?     Why  ? 
Fold  a  filter  paper  as  shown 

in  Fig.  16  and  open  it  into  a 

cone  having  three  thicknesses  of 

paper  on  one  side  and  one  on 

the  other.     Fit  it  into  a  funnel, 

moisten  with  a  little  water  and 

press  the  paper  snugly  against  the  sides  of  the  funnel.  Sup- 
port the  funnel  in  a  ring  stand, 
placing  a  beaker  beneath  it. 

Stir  up  the  mixture  previ- 
ously prepared  and  pour  it 
gradually  upon  the  filter  paper 
in  the  funnel,  always  keeping 
the  liquid  well  below  the  top  of 
the  paper.  To  avoid  spattering 
and  prevent  drops  running  down 
the  sides  of  the  beaker,  hold  the 
middle  of  a  glass  rod  against  the 
edge  of  the  beaker  and  pour 
the  liquid  along  the  rod  on  to 
the  side,  not  the  tip,  of  the  filter 
FIQ.  17.  ,  paper,  as  shown  in  Fig.  17. 


FIG.  16. 


42          LABORATORY  MANUAL  IN   CHEMISTRY 

This  process  is  called  filtration.  The  liquid  which  runs 
through  it  is  called  the  filtrate  :  the  substance  remaining 
in  the  filter  is  the  residue.  Ascertain  by  tasting  whether 
the  salt  is  in  the  residue  or  the  filtrate.  Can  dissolved 
substances  be  separated  from  liquids  by  filtration  ?  What 
substances  can  be  separated  by  filtration  ?  Suggest  prac- 
tical uses  of  the  process  of  filtration. 

(<i)    Distillation. 

Add  sufficient  salt  and  red   ink  or  permanganate  to 
about  150  ccm.  of  water  to  give  it  a  distinct  taste  and 


FIG.  18. 

color.  Place  the  liquid  in  the  boiling  flask  and  connect 
the  flask  with  the  condenser  as  shown  in  Fig.  18.  Connect 
the  lower  opening  of  the  jacket  of  the  condenser  to  a 
water  tap,  so  that  the  flow  of  water  will  be  in  the  direction 
indicated  by  the  arrows.  Turn  on  the  water,  and  as  it 
issues  from  the  upper  outlet,  conduct  it  by  means  of 
rubber  tubing  to  the  sink.  Heat  the  flask  on  a  wire 
gauze  until  the  water  boils.  Note  carefully  and  describe 
what  happens.  This  process  is  called  distillation. 


EXPERIMENTS  43 

Allow  the  first  few  ccm.  of  the  distillate,  i.e.  the 
liquid  that  condenses,  to  go  to  waste,  as  this  may  con- 
tain dust  and  impurities  washed  out  of  the  condenser. 
Collect  the  remainder  of  the  distillate  in  a  clean  flask 
or  beaker,  continuing  the  process  until  there  is  enough 
to  test.  Note  the  color,  odor,  and  taste  of  distilled 
water.  Where  is  the  salt  and  coloring  matter  ?  What 
class  of  substances  may  be  removed  by  distillation  ? 
What  class  might  not  be  removed  in  this  way  ?  For 
drinking  purposes  is  distillation  a  better  method  of  puri- 
fying  water  than  filtration?  State  several  reasons  why. 
Suggest  practical  uses  of  the  process  of  distillation. 

EXP.  22.    HOW  HEAT   AFFECTS   SOLUBILITY 

Materials.  Crystallized  copper  sulfate  (blue  vitriol), 
salt,  potassium  chlorate,  and  alum. 

Apparatus.  Mortar  and  pestle.  Test  tubes.  A  beaker 
of  boiling  water.  Four  small  1  gram  measures,*  one  for 
each  of  the  substances  mentioned  above. 

Procedure.  Put  exactly  10  ccm.  of  cold  water  into  a 
test  tube,  and  to  it  add  very  finely  powdered  copper  sul- 
fate in  successive  portions  of  1  g.  each,  as  long  as  it  dis- 
solves. Shake  the  test  tube  continually  tc  aid  solution. 
When  no  more  will  dissolve,  the  solution  is  said  to  be 
saturated.  What  is  the  solubility  of  copper  sulfate  in 
water  at  room  temperature  ? 

Heat  the  saturated  solution  of  copper  sulfate  by  placing 
the  test  tube  in  boiling  water  and  again  add  powdered 
copper  sulfate  in  portions  of  1  g.  each  until  no  more  will 
dissolve.  How  many  additions  of  copper  sulfate  are 
required  to  saturate  the  solution  ?  What  is  the  solubility 
of  copper  sulfate  in  water  at  100°  ?  How  is  the  solubility 
of  copper  sulfate  affected  by  rise  in  temperature  ? 
*  See  Suggestions  to  Teachers. 


44    LABORATORY  MANUAL  IN  CHEMISTRY 

Cool  the  solution  of  copper  sulfate  by  holding  the  test 
tube  in  running  water.  Explain  the  result. 

Repeat  the  above  procedure,  some  students  using  salt, 
others  potassium  chlorate,  others  alum  in  place  of  copper 
sulfate.  Does  heat  affect  the  solubility  of  all  substances 
alike  ? 

NOTE.  When  heat  increases  solubility,  cooling  of  a  saturated 
solution  causes  supersaturation.  The  normal  tendency  of  a  super- 
saturated solution  is  to  separate  out  immediately  the  excess  of  the 
solute,  i.e.  of  the  dissolved  substance.  With  certain  substances,  how- 
ever, this  separation  seems  to  "  stick  "  and  some  supersaturated  solu- 
tions may  exist  for  some  time  before  separation  of  the  excess  of  the 
solute  takes  place,  as  is  shown  in  the  next  experiment. 

EXP.  23.    SUPERSATURATION 

Instructor's  Experiment 

Materials.  Sodium  sulfate  (Glauber's  salt),  or  sodium 
thiosulfate  (hypo). 

Apparatus.  A  beaker.  2-3  test  tubes  with  tightly 
fitting  corks.  A  thermometer. 

Procedure.  Pulverize  about  100  g.  of  sodium  sulfate, 
place  it  in  the  beaker,  add  about  25  com.  of  water,  warm 
to  30°-35°,*  and  maintain  at  this  temperature  for  about 
15  minutes,  stirring  to  hasten  solution.  If  all  of  the 
sodium  sulfate  dissolves  readily,  add  more  until  the  solu- 
tion is  saturated.  If  some  remains  undissolved,  add 
water,  1  com.  or  so  at  a  time,  until  everything  has  gone 
into  solution.  Rinse  out  the  test  tubes,  including  the 
corks,  with  water  and  invert  them  so  that  they  may  drain. 
Pour  the  solution  of  sodium  sulfate,  saturated  at  30°-32°, 
into  the  test  tubes,  cork  immediately,  and  let  stand  undis- 
turbed until  thoroughly  cold.  The  water  then  holds  in 

*  The  solubility  of  sodium  sulfate  is  greater  at  32°  than  at  any  other 
temperature. 


EXPERIMENTS  45 

solution  an  excess  of  sodium  sulfate  beyond  the  amount 
which  would  dissolve  at  room  temperature.  The  solution 
is  supersaturated,  yet  no  crystals  of  sodium  sulfate  ordi- 
narily appear. 

Shake  one  of  the  test  tubes  and  describe  what  happens. 
When  supersaturated  solutions  are  disturbed,  separation 
of  the  solid  usually  takes  place. 

Cautiously  remove  the  cork  from  another  test-tube  and 
drop  a  minute  crystal  of  sodium  sulfate  into  the  solution. 
Notice  how  from  this  as  a  nucleus  the  crystals  grow  in  all 
directions  until  the  contents  of  the  test  tube  become  prac- 
tically solid. 

Sodium  sulfate  is  one  of  the  common  substances  present 
as  dust  in  the  atmosphere.  Why  was  it  necessary  to 
keep  the  tubes  corked  ? 

Repeat  the  whole  experiment,  if  time  permits,  using 
50  g.  of  sodium  thiosulfate  (hypo).  Heat  the  crystals 
gently  in  a  test  tube  and  they  will  dissolve  in  the  water 
which  they  contain,  forming  a  saturated  solution.  Cool 
the  test  tube  in  running  water  to  room  temperature,  intro- 
duce a  small  crystal  of  hypo  and  watch  the  crystals  grow. 

EXP.  24.    SOLUTIONS  OF  GASES 

Materials.     A  syphon  or   bottle  of   carbonated  water. 
Apparatus.      Thermometer.      Beakers.      Gauze.     Ring 
stand. 

Procedure,  (#)  How  pressure  affects  the  solubility  of 
gases. 

Press  the  lever  and  draw  about  50  ccm.  of  water  from 
the  syphon  into  a  beaker.  What  causes  the  water  to 
leave  the  syphon  ?  Note  the  separation  of  gas  from  the 
solution,  causing  the  bubbling  or  effervescence.  Was  the 
water  when  drawn  from  the  bottle  saturated,  unsaturated, 


46  LABORATORY  MANUAL   IN  CHEMISTRY 

or  supersaturated  with  gas  ?  How  is  the  pressure  on  th« 
solution  remaining  in  the  bottle  affected  when  liquid  is 
removed  from  the  syphon?  Do  you  see  any  indication  of 
this  ?  How  does  change  of  pressure  affect  the  solubility 
of  the  gas  ? 

(5)  How  temperature  affects  the  solubility  of  gases. 

Set  the  beaker  and  its  contents  on  a  gauze  on  a  ring 
stand  and  warm  with  a  burner.  Test  the  temperature 
with  the  thermometer  and  do  not  heat  to 'the  boiling  point 
of  water.  How  does  the  rise  in  temperature  affect  the 
solubility  of  the  gas  ?  Contrast  this  effect  with  the  effect 
of  a  rise  in  temperature  on  the  solubility  of  solids. 

Draw  100  ccm.  of  cold  water  from  the  tap  and  warm  it 
over  the  burner.  How  do  you  account  for  the  formation 
of  small  bubbles  on  the  inside  of  the  beaker. 

When  a  glass  of  cold  water  is  allowed  to  stand  for 
some  time,  small  bubbles  appear,  clinging  to  the  glass. 
Explain  their  formation. 

EXP.  25.    CRYSTALLIZATION 

Materials.  Copper  sulfate.  Potassium  dichromate. 
Alum.  Salt. 

Apparatus.     Beakers.     Funnels.     Filters. 

Procedure.  From  the  results  of  Experiment  22  calcu- 
late how  much  water  will  be  needed  to  make  a  solution  of 
50  g.  of  copper  sulfate  saturated  at  100°,  Put  together  the 
water  and  copper  sulfate,  heat  to  boiling,  and  see  whether 
your  calculation  was  approximately  correct.  If  some  solid 
remains  undissolved,  add  a  little  more  water.  If  all  the 
copper  sulfate  goes  into  solution,  and  you  have  reason  to 
believe  that  you  added  too  much  water,  evaporate  the 
solution  over  a  Burisen  burner  or  on  a  water  bath  until  a 
solid  begins  to  form  around  the  edges  or  in  the  solution. 


EXPERIMENTS  47 

A  water-bath  consists  of  a  vessel  containing  water 
that  is  kept  boiling  by  a  burner  placed  beneath.  The 
steam  from  this  vessel  transmits  heat  at  100°  to  another 
vessel  placed  in  or  on  the  first.  A  dish  containing  the 
liquid  to  be  evaporated  set  on  top  of  a  beaker  of  water, 
boiling  slowly,  is  a  simple  form  of  water-bath.  A  common 
household  form  is  the  double  boiler  used  for  cooking  sub- 
stances that  readily  burn. 

If  the  saturated  copper  sulfate  solution  is  not  clear,  it 
may  be  filtered,  but  the  addition  of  a  few  drops  of  sulfuric 
acid  will  usually  render  the  solution  perfectly  clear  with- 
out interfering  with  the  resulting  product. 

Put  a  little  of  the  liquid  into  a  test  tube,  cool  it  in 
running  water,  and  shake. 

Cover  the  rest  of  the  liquid  in  the  beaker  and  set  it  away 
to  cool.  How  do  the  resulting  crystals  differ  in  the  two 
cases?  How  does  rapidity  of  formation  seem  to  influence 
their  size  ?  (The  smaller  crystals  are  likely  to  be  purer.) 

Prepare  hot  solutions  of  50  g.  of  alum,  30  g.  of  potas- 
sium dichromate,  and  20  g.  of  salt,  each  in  50  ccm.  of 
water,  some  students  preparing  one,  others  another.  Cover 
the  beakers  containing  the  solutions  and  set  them  away  to 
cool.  After  some  time  examine  the  resulting  crystals. 
Remove  some  of  the  most  perfect  crystals,  placing  them  on 
pieces  of  filter  paper  to  dry.  Describe  any  differences  in 
form  which  you  notice.  Remove  covers  from  the  beakers 
and  allow  the  solutions  to  evaporate  until  the  original 
substances  are  recovered. 


EXP.  26.    WATER  IN  CRYSTALS 

Materials.  Crystals  of  copper  sulfate,  sodium  sulfate, 
potassium  chlorate,  sodium  carbonate,  alum,  salt.  Calcium 
chlorid.  Sodium  hydroxid.  Cobalt  chlorid  solution. 


48  LABORATORY  MANUAL  IN  CHEMISTRY 

'  Apparatus.     Dry   test   tubes.     Glass   plates   or   watch 
glasses. 

Procedure,     (a)    Water  in  crystals. 

1.  Examine  carefully  a  crystal  of  copper  sulfate  (blue 
vitriol).     Do  you  notice  any  evidence  of  moisture  about  it  ? 

Place  a  copper  sulfate  crystal  weighing  about  1  g.  in  a 
clean  dry  test  tube,  and  heat  it  gently.  Describe  what 
happens.  What  appears  on  the  cool  sides  of  the  test 
tube  ?  Test  it  and  see  if  it  is  water.  From  what  source 
must  this  have  come  ?  Do  you  think  it  was  chemically 
combined  or  just  mixed  with  the  copper  sulfate  ? 

When  the  copper  sulfate  undergoes  no  further  change 
on  gently  heating  allow  the  residue  to  cool  and  moisten  it 
with  a  drop  or  two  of  water.  What  effect  do  you  notice  ? 
The  change  in  color  is  due  to  the  formation  of  minute 
crystals  of  the  original  copper  sulfate.  The  heated  copper 
sulfate  *  unites  with  water  to  form  blue  vitriol  or  crystal- 
lized copper  sulfate. 

To  obtain  larger  crystals,  dissolve  the  residue  in  a  little 
warm  water,  and  allow  the  liquid  to  evaporate  sponta- 
neously. Compare  the  crystals  which  form  with  the 
original  substance.  Can  you  detect  any  difference  ? 

2.  Moisten  some  filter  papers  with  a  little  cobalt  chlorid 
solution  and  allow  them  to  dry  spontaneously.     The  pink 
color  is  due  to  crystals  of  cobalt  chlorid  which  contain 
water.     Warm  three  or  four  of  the  filter  papers  over  a 
burner  and  note  the  change  of  color  due  to  driving  out  the 
water  from  the  crystals. 

Moisten  one  of  the  blue  papers  with  a  drop  of  water  and 
explain  the  action.  Breathe  upon  another  and  allow  a 
third  to  stand  exposed  to  the  air.  This  procedure  is  used 
as  a  test  for  water. 

Blue  cobalt  chlorid  paper  acts  as  a  barometer  to  indicate 
*  This  procedure,  as  well  as  that  given  in  2,  is  used  as  a  test  for  water. 


EXPERIMENTS  49 

whether  the  air  contains  much  or  little  water  vapor.  In 
hot  dry  regions  it  will  be  blue,  while  a  moist  atmosphere 
is  indicated  by  the  pink  color.  Try  it  for  your  locality  at 
various  times  of  the  year. 

3.  Heat  dry  crystals  of  the  other  substances  and  ascer- 
tain whether  they  contain  water.  Many  (not  all)  crystals 
contain  water. 

(5)    Water  in  crystals  held  chemically. 

Note  the  taste  of  alum.  Heat  gently  on  an  iron  pan  or 
on  an  evaporating  dish  a  crystal  of  alum  about  the  size  of  a 
hazelnut.  When  the  alum  undergoes  no  further  change, 
turn  it  over  so  as  to  heat  the  other  side.  Then  remove 
the  flame. 

When  the  piece  of  "  burnt  alum  "  is  cool,  break  it  open, 
and  taste  a  bit  of  the  inside.  Is  it  any  longer  alum  ? 
What  kind  of  a  change  was  occasioned  by  the  loss  of  the 
water  ?  Was  the  water  in  .  the  crystals  chemically  com- 
bined or  were  the  crystals  merely  a  mixture  of  water  and 
"  burnt  alum  "  ? 

Put  the  "  burnt  alum  "  in  a  test  tube,  add  to  it  about 
ten  times  its  volume  of  water,  and  keep  the  whole  near  the 
boiling  point  for  about  five  minutes.  Then  cool  by  hold- 
ing the  test  tube  in  running  water,  and  taste  the  liquid. 
What  substance  does  the  liquid  now  contain?  How  was 
it  formed  ? 

What  distinction  can  you  draw  between  the  expres- 
sions "  blue  vitriol "  and  "  copper  sulfate  "  ?  Between 
"  Glauber's  salt "  and  "  sodium  sulfate  "  ?  Between  "  soda 
crystals  "  and  "  sodium  carbonate  "  ?  Is  there  any  differ- 
ence between  "  salt "  and  "  sodium  chlorid  "  ? 

(c)  Efflorescence. 

On  clean  glass  plates  expose  clear  crystals  of  sodium 
sulfate  and  sodium  carbonate,  allowing  the  crystals  to 


50          LABORATORY  MANUAL  IN  CHEMISTRY 

stand  several  days  if  necessary.  Then  note  what  has 
happened.  What  becomes  of  the  water  which  the  crys- 
tals contained  ?  Why  should  bottles  containing  crystals 
be  kept  corked  ? 

[d)  Deliquescence. 

Expose  on  glass  plates  overnight  pieces  of  calcium 
chlorid  and  of  sodium  hydroxid.  Examine  the  sub- 
stances the  next  day.  From  what  source  must  the  water 
have  come  ?  Calcium  chlorid  is  sprinkled  on  roads  to 
prevent  them  from  getting  dusty.  Explain  its  action. 

EXP.  27.     PURIFICATION  BY  CRYSTALLIZATION 

Materials.  Alum.  Copper  sulphate.  Potassium  sul- 
fate.  Aluminum  sulfate. 

Procedure.  (a)  The  separation  of  alum  from  copper 
sulfate. 

Take  50  g.  of  alum,  and  for  an  impurity  mix  with  it 
10  g.  of  copper  sulfate.  Powder  the  mixture  and  dis- 
solve it  in  50  ccm.  of  boiling  water.  Filter  the  solution 
if  it  is  not  clear.  Set  the  beaker  containing  the  solution 
in  a  dish  of  cold  water.  Stir  the  contents  of  the  beaker 
with  a  glass  rod,  and  change  the  water  in  the  dish  if  it 
becomes  warm.  When  the  liquid  is  cool,  pour  the  con- 
tents of  the  beaker  upon  a  filter.  What  is  the  color  of 
the  filtrate  ?  What  does  this  color  indicate  ? 

Wash  the  crystals  on  the  filter  by  pouring  over  them 
several  times  10  ccm.  of  cold  water,  allowing  each  por- 
tion to  drain  off  entirely  before  adding  another  portion. 
Continue  washing  until  the  wash  water  is  no  longer 
blue.  Then  lay  3-4  filter  papers,  one  on  top  of  the  other, 
on  the  table,  spread  out  the  crystals  on  the  upper  one 


EXPERIMENTS  51 

and  dry  them  by  pressing  with  2-3  other  filter  papers. 
When  the  moisture  has  been  absorbed  by  the  paper,  ex- 
amine the  crystals  and  taste  them.  Of  what  do  they 
seem  to  consist?  Can  you  see  any  of  the  other  sub- 
stance ? 

A  copper  compound  mixed  with  ammonium  hydroxid 
gives  a  blue  liquid.  Dissolve  a  little  of  the  crystallized 
substance  in  a  little  warm  water  and  add  ammonium 
hydroxid.  If  the  test  for  copper  indicates  its  presence, 
dissolve  the  crystals  in  as  little  hot  water  as  possible, 
and  recrystallize  the  alum. 

NOTE.  While  many  substances  form  pure  crystals  in  solutions 
containing  more  than  one  substance,  and,  therefore,  may  be  separated 
from  each  other  by  crystallization,  others  may  not  be  separated  in 
this  way  because  they  form  mixed  crystals  or  crystals  of  new  sub- 
stances, as  shown  in  (6). 

(7>)  Substances  not  separable  by  crystallization. 

Dissolve  3.5  g.  of  potassium  sulfate  and  13  g.  of  alumi- 
num sulfate  in  about  40  com.  of  hot  water,  and  set  the 
solution  away  to  cool.  When  crystals  have  formed,  re- 
move them  and  by  their  taste  identify  them.  Are  these 
crystals  a  new  substance  or  are  they  the  same  as  one  of 
the  ingredients  in  the  mixture  ? 


EXP.  28.     REACTIONS  RUN  TO   EQUILIBRIUM  UNLESS 
PREVENTED  BY   SOME  FACTOR 

Materials.  Cone,  nitric  (HNO3),  sulfuric  (H2SO4),  and 
hydrochloric  (HC1)  acids.  Potassium  nitrate,  KNO3. 
Potassium  hydrogen  sulfate,  KHSO4.  Potassium  chro- 
mate,  K2CrO4.  Sodium  carbonate,  Na2CO3.  Lead  nitrate, 
Pb(NO3)2.  Pieces  of  copper. 

Apparatus.     Beakers.     Test  tubes.     Stirring  rods. 


52    LABORATORY  MANUAL  IN  CHEMISTRY 

Procedure,  (a)  Reactions  running  to  equilibrium,  not  to 
completion. 

1.  Test  and  see  that   solutions   of   potassium   nitrate, 
potassium   hydrogen   sulfate    and    sulfuric   acid    do    not 
attack  copper  but  that  nitric  acid  does. 

2.  To   10  ccm.  of   water  in  a  beaker   add    cautiously 
10  ccm.  of  cone.  H2SO4  and  mix  thoroughly.     Make  a 
saturated  solution  by  heating  20  g.  of  potassium  nitrate 
with  10  ccm.  of  water  and  divide  into  two  equal  portions. 

To  half  of  the  potassium  nitrate  solution  add  5  ccm. 
of  the  H2SO4  (1:1)  solution.  Pour  a  few  drops  of  the 
mixture  upon  copper  and  note  the  action,  warming  if 
necessary.  What  causes  this  action?  Stand  the  remain- 
der aside  to  cool  and  crystallize.  Note  the  formation  of 
clear  needles  of  potassium  nitrate. 

3.  Heat  the  other  half  of  the  potassium  nitrate  solution 
(prepared  above)  if  necessary  to  keep  the  KNO3  in  solu- 
tion   and   add   10   ccm.    of   the    H2SO4    (1:1)    solution. 
Pour  a  few  drops  of  the  mixture  upon  copper  and  note 
the  action.     What   causes   this   action  ?     Stand   the   re- 
mainder aside  to  cool  and  crystallize  (if  necessary  over- 
night).    Note  the  formation  of  opaque  crystals  of  potas- 
sium hydrogen  sulfate. 

Discussion.  Between  potassium  nitrate  and  sulfuric 
acid  the  only  reaction  which  can  take  place  under  the 
condition  of  these  experiments  is  represented  by  the 
equation : 

potassium        hydrogen  hydrogen        potassium  hy- 

nitrate      +     sulfate      < — >     nitrate     -f-  drogen  sulfate 
KNO8      +      H2SO4     «->     HNOt     +        KHSO4 

That  some  HNO8  is  formed  in  (2)  is  indicated  by  the 
fact  that  the  mixture  attacks  copper;  for,  of  the  four  sub- 
stances represented  in  the  equation,  HNO3  is  the  only 


EXPERIMENTS  53 

reagent  which  will  attack  copper.  This  proves  that  some 
KNO3  has  reacted  with  H2SO4  to  form  HNO3.  Yet,  on 
cooling,  potassium  nitrate  separates  from  the  solution, 
proving  that  all  of  the  KNO3  has  not  reacted  with  the 
H2SO4  present.  In  other  words,  the  reaction  does  not  run 
to  completion  but  to  equilibrium,  all  four  of  the  sub- 
stances being  present  in  solution. 

In  (3)  twice  the  proportion  of  sulfuric  acid  is  added 
that  was  present  in  (2).  The  mass  action  of  the  H2SO4 
on  the  KNOg  causes  the  reaction  to  run  much  further 
toward  completion  than  in  (2),  as  is  indicated  by  the  crys- 
tallization of  KHSO4  instead  of  KNO3  from  the  solution. 
All  four  substances  are  still  present  in  the  mixture  but 
there  is  more  KHSO4  than  KNO3. 

When  none  of  the  substances  present  in  a  reacting  mixture 
are  removed  from  the  sphere  of  action,  reactions  run  to 
equilibrium. 

Nitric  acid  boils  at  120.5°,  H2SO4  at  330°;  KNO3  and 
KHSO4  are  volatile  only  at  higher  temperatures.  By 
heating  up  the  mixtures  in  (2)  and  (3)  water  will  boil 
away  first.  When  the  temperature  rises  above  121°, 
HNO3  will  become  a  gas  and  boil  away.  What  effect 
will  this  have  on  the  reaction  ?  Why  ?  Before  answer- 
ing this  question  perform  (5)  if  necessary. 

(&)  Reaction  running  to  completion. 

1.  Equilibrium  prevented  by  the  formation  of  a  gaseous 
substance. 

To  10  ccm.  of  water  add  a  drop  or  two  of  HC1.  Taste 
the  solution  and  note  one  of  the  characteristic  properties 
of  acids. 

Dissolve  15  g.  of  sodium  carbonate  crystals  (or  8  g.  of 
anhydrous  Na2CO3)  in  25  ccm.  of  boiling  water.  Dilute 
10  ccm.  of  cone,  HCl  with  an  equal  volume  of  water  and 


54         LABORATORY  MANUAL  IN  CHEMISTRY 

heat  to  boiling.  Remove  from  the  flame  and  add  gradu 
ally  the  sodium  carbonate  solution  until  a  further  slight 
addition  of  the  latter  produces  no  effervescence.  Then 
cool  the  liquid  and  taste  it.  Is  HC1  any  longer  present  ? 
What  common  substance  seems  to  have  taken  its  place  ? 
Do  you  judge  that  any  gaseous  substance  was  formed 
during  the  reaction  ?  Why  ? 

The  equation  representing  the  reaction  which  has  taken 
place  is 

f  sodium         hydrogen        sodium        water        carbon 

carbonate  +     chlorid    — >  chlorid  4-  +  dioxid 

Na2C03    +      2  HC1    ->  2  NaCl  +  H2O   +     CO2 

Which  of  the  reaction  products  escaped  as  a  gas?  Ex- 
plain in  detail  how  the  formation  of  a  gaseous  substance 
causes  the  reaction  to  run  to  completion. 

2.  Equilibrium  prevented  by  the  formation  of  an  in- 
soluble substance. 

Dissolve  about  1  g.  of  potassium  chromate  in  100  ccm. 
of  water  and  2  g.  of  lead  nitrate  in  about  20  ccm.  of  water 
and  heat  both  solutions  to  boiling.  Add  half  of  the  lead 
nitrate  solution  to  the  potassium  chromate  solution,  stir 
thoroughly  and  allow  the  mixture  to  stand  for  a  few 
minutes.  When  the  precipitate  has  settled,  add  to  the 
clear  liquid  above  it  a  few  drops  of  the  lead  nitrate  solu- 
tion. If  a  precipitate  forms,  add  1-2  ccm.  more,  stir  and 
allow  to  settle  once  more.  Test  the  clear  liquid  as  before 
and  add  the  lead  nitrate  solution,  a  little  at  a  time,  as  long 
as  a  precipitate  forms.  Then  filter  the  solution.  If  the 
filtrate  is  colored,  add  more  lead  nitrate  and  filter  again. 

All  chromates  are  intensely  colored.  Judging  from 
the  color  of  the  filtrate,  does  it  contain  any  chromate  ? 
Judging  by  the  color,  where  is  the  chromate  ?  Did  the 
reaction  run  to  equilibrium  or  to  completion  ?  By  evapo- 


EXPERIMENTS 


55 


rating  the  filtrate,  needle-like  crystals  of  potassium  nitrate 

could  be  obtained.     Where  did  the  potassium  come  from  ? 

Where   the    nitrate  ?      The    equation    representing    the 

change  is  : 

potassium  lead  lead  potassium 

chromate   +     nitrate     —  >  chromate  -f-    nitrate 


K2CrO4 


Pb(NO3)2  ->•  PbCrO4  +    2  KNO3 


EXP.  29.    HYDROGEN  CHLORID,  HC1 

Materials.  Salt,  NaCl.  Cone,  sulfuric  acid,  H2SO4. 
Magnesium  ribbon.  Manganese  dioxid,  MnO2.  Copper 
oxid,  CuO.  Nitric  acid,  HNO3.  Silver  nitrate  (AgNO3) 
solution.  Ammonia  water  (ammonium  hydroxid),  NH4OH. 
Litmus  paper. 

Apparatus.  A  250  com. 
flask  fitted  with  thistle  and 
exit  tubes  as  shown  in  Fig. 
19.  A  bottle.  Piece  of  card- 
board with  hole  in  center. 

Procedure,  (#)  Prepara- 
tion. 

To  10  ccm.  of  water  in 
a  beaker  add  cautiously  15 
ccm.  of  cone.  H2SO4  and 
allow  the  mixture  to  cool. 
Set  up  the  apparatus  as 
shown  in  Fig.  19.  Place 
about  25  g.  of  salt  in  the 
flask,  insert  the  stopper,  and 

through  the  thistle  tube  pour  in  the  H2SO4  solution  previ- 
ously prepared.  Hydrogen  chlorid  is  evolved  at  once  but 
the  flask  may  be  warmed  if  necessary  to  hasten  action. 

Complete  the  equation  :  H2SO4  4-  2  NaCl  -> 


FIG.  19. 


56  LABORATORY  MANUAL  IN   CHEMISTRY 

(5)  Properties. 

Is  the  gas  colorless  and  invisible  while  (1)  inside  the 
flask  ;  (2)  outside  the  flask  or  bottle  as  it  escapes  into  the 
air  ?  Blow  gently  across  the  top  of  the  bottle  from  which 
the  gas  is  escaping.  What  causes  the  change  in  the  appear- 
ance of  the  gas?  In  answering  this  question  recall  what 
happens  to  a  cold  window  pane  when  breathed  upon. 
Note  the  odor  of  the  gas.  Hold  a  moistened  finger  for 
an  instant  in  the  bottle  of  gas,  and  then  touch  the  finger 
to  the  tongue.  Bring  a  lighted  match  into  the  gas. 
Does  it  burn  or  support  combustion  ? 

Withdraw  the  delivery  tube  from  the  bottle  and  insert 
it  as  far  as  possible  in  a  test  tube  and  collect  some  gas  by 
downward  displacement.  Close  the  test  tube  with  the 
thumb  and  invert  in  a  dish  of  water.  Remove  thumb 
and  explain  the  result.  Why  not  collect  the  gas  over 
water  ? 

(e)  Hydrochloric  acid,  HC1. 

Put  about  20  ccm.  of  water  into  the  bottle  and  again 
introduce  the  delivery  tube,  keeping  the  end  just  above 
the  surface  of  the  water.  Continue  the  action  as  long  as 
gas  is  readily  absorbed. 

Prove  the  identity  of  the  solution  of  hydrogen  chlorid 
thus  obtained  with  the  hydrochloric  acid  of  the  laboratory 
bottle  by  making  the  first  four  of  the  following  tests  on 
each  liquid. 

1.    Note  the  effect  of  each  on  blue  and  red  litmus  paper. 

2o    Dilute  considerably  and  note  the  taste. 

3.  Put  10  ccm.  in  a  small  test-tube  and  fill  with  dis- 
tilled water.  Invert  in  a  dish  of  water  and  test  the  action 
of  magnesium  on  each  liquid,  as  directed  in  Exp.  17,  (V). 
Are  the  reactions  the  same  in  each  case  ?  What  is  one 
constituent  of  hydrochloric  acid  ? 


EXPERIMENTS  57 

4.  Heat  10    com.    in   a   test  tube  with   a   little   man- 
ganese   dioxid.     Are    the    reactions    the    same   in   each 
case  ?     The  other  constituent  of  hydrochloric  acid,  thus 
liberated,  is  chlorin. 

5.  Shake  about  1  g.  of  copper  oxide  with  10  ccm.  of 
hot  water.     Is  it  soluble  ?     Add  5  ccm.  of  HC1  and  heat 
if  necessary.    Is  there  any  reaction  ?     How  do  you  know? 
The  substance  formed  is  copper  chlorid,  CuCl2.     Write 
an  equation  showing  its  formation. 

6.  To  a  dilute  solution  of  hydrogen  chlorid  or  other 
chlorid,  add  a  little  nitric  acid  and  a  few  drops  of  silver 
nitrate  solution.      Note  the  character  of  the  precipitate 
which  appears.     To  one  portion  of  the  liquid  containing 
the  precipitate  add  ammonia  water  until  the  solution  will 
turn  red  litmus  paper  blue.     What  happens  to  the  pre- 
cipitate ? 

Other  soluble  chlorids  besides  hydrogen  chlorid  give 
these  same  reactions.  This  procedure  is  used  as  a  test 
for  chlorids. 

The  taste  of  hydrochloric  acid,  its  action  on  litmus 
paper  and  on  many  metals  and  oxids  are  properties  pos- 
sessed by  acids  in  general.  State  these  general  properties 
of  acids. 


EXP.  30.    CHLORIN 

Materials.  Cone,  hydrochloric  acid,  HC1.  Manganese 
dioxid,  MnO2.  Yellow  phosphorus.  Thin  copper  foil. 
Charcoal.  Turpentine.  A  candle  twisted  into  a  wire 
for  a  holder.  Potassium  hydroxid  (KOH)  solution. 

Apparatus  as  shown  in  Fig.  20.  3-4  bottles  having 
the  same  size  neck  interchangeable  with  A.  Wooden 
block.  Beaker.  A  hydrogen  generator  with  a  clay  pipe- 
stem  tip. 


58 


LABORATORY  MANUAL  IN  CHEMISTRY 


Combustion  spoon.     Filter  paper.       Pieces  of  cardboard 
or  glass  plates. 

NOTE.     Chlorin  is  a  very  irritating  gas,  the  effects  of  which  may 
be  counteracted  by  inhaling  .the  fumes  of  alcohol  sprinkled  on  a  hand- 
kerchief.    This    whole    experiment 
should  be  performed  under  a  hood 
or  in  a  good  draft. 

Procedure,    (a)  Preparation. 

Place  about  30  g.  of  manga- 
nese dioxid  in  the  flask  and  set 
up  the  apparatus  as  shown  in 
Fig.  20.  Through  the  thistle 
tube  introduce  about  50  ccm. 
of  cone.  HC1.  Chlorin  will  be 
evolved  at  once  but  the  flask 
may  be  warmed  when  neces- 
sary to  hasten  the  reaction. 
To  prevent  chlorin  from  get- 
ting into  the  room,  cover  the  end  of  the  exit  tube  in  the 
beaker  with  water.  When  this  becomes  yellowish,  show- 
ing that  it  is  nearly  saturated,  add  potassium  hydroxid 
solution  until  the  color  disappears.  Keep  the  resulting 
liquid  for  the  next  exercise. 

Fill  6-8  bottles  with  the  gas  by  downward  displacement, 
removing  A  as  soon  as  it  takes  on  a  yellowish  color  and 
substituting  one  of  the  other  bottles.  Cover  each  bottle, 
when  removed,  with  a  cardboard  or  glass  plate.  As  soon 
as  you  have  collected  one  or  two  bottles  of  gas,  begin  to 
perform  the  experiments,  refilling  these  bottles  for  the 
later  experiments. 

Complete  the  equation  :    MnO2  -f  4  HCl-> 
Is  MnO2  an  oxidizing  or  reducing  agent  ?     What  other 
substances  that  you  have  worked  with  do  you  think  might 
be  substituted  for  MnO0  in  this  reaction  ? 


FIG.  20. 


EXPERIMENTS  59 

(5)  Physical  properties. 

Note  the  color  and  odor  of  chlorin.  Compare  with  the 
color  and  odor  of  the  water  in  the  beaker  in  which  the 
exit  tube  dips.  Is  chlorin  soluble  in  water  ? 

(<?)    Chemical  properties. 

1.  Dry  a  small  piece  of  phosphorus,  observing  the  pre- 
cautions mentioned  on  page  15.     Place  it  in  a  combus- 
tion spoon  and,  without  lighting  it,  introduce  it  into  a 
bottle  of  chlorin.     What  happens  ?    Phosphorus  trichlorid, 
PC13,  is  formed.      Write   an  equation  for   the   reaction 
taking  place. 

2.  Heat  the  strip  of  copper  foil  and  before  it  has  had 
time  to  cool  introduce  it  into  another  bottle  of  chlorin. 
What    happens  ?     Copper    chlorid,    CuCl2,    is   formed ; 
write  the  equation. 

3.  After   testing   its  purity,  the  instructor  will   light 
the  hydrogen  as  it  issues  from  the  clay  tip  attached  to 
a    hydrogen    generator,    and    introduce    the    flame    into 
another    bottle    of    chlorin.     Does    chlorin    support    the 
combustion    of   hydrogen  ?     Notice    any    change    in   the 
character  of  the  flame.     Allow  the  burning  to  continue 
for  some  time,  and  then  withdraw  the  flame  if  it  is  not 
already   extinguished.     Hold  a  moistened   finger   in   the 
gas  in  the  bottle  and  touch  it  to  the  tongue.     Note  the 
effect   of  this   gas  on  a  moistened  piece  of  blue  litmus 
paper  and  blow  gently  into  the  bottle.     What  happens? 
What  is  the  ash,  i.e.  the  product  formed,  when  hydrogen 
burns   in   chlorin?      Write  an   equation   expressing   the 
reaction. 

4.  Set  fire  to  a  small  piece  of  charcoal,  noting  how  it 
burns  in  the  air.     Then  introduce  it,  still  glowing,  into 
a  bottle  of  chlorin.     Does  chlorin  support  the  combustion 
of  carbon? 


60          LABORATORY  MANUAL  IN  CHEMISTRY 

5.  The  substances  ordinarily  burned  for  light  or  heat 
consist  largely  or  entirely  of  carbon  and  hydrogen.     A 
candle  and  turpentine  are  of  this  nature.     To  ascertain 
the  action  of  chlorin  on  these  substances  containing  both 
hydrogen  and  carbon  proceed  as  follows : 

Light  a  candle,  and  notice  how  it  burns  in  the  air. 
By  means  of  a  wire  lower  it,  still  lighted,  into  a  bottle 
of  chlorin.  Though  the  candle  continues  to  burn  for 
a  time,  how  does  the  character  of  the  flame  change  ? 
What  becomes  of  the  carbon  in  the  candle?  Blow 
gently  across  the  mouth  of  the  bottle.  What  becomes 
of  the  hydrogen  in  the  candle  ? 

If  time  permits,  make  a  similar  test  with  a  small 
flame  of  illuminating  gas  burning  in  chlorin. 

6.  Heat  5  ccm.  of  turpentine  to  boiling  in  a  test  tube, 
taking  care  that  it  does  not  catch  fire.     Pour  it  over 
a  large  piece  of  filter  paper,  then  drop  into  a  bottle  of 
chlorin  before  the  turpentine  has  time  to  cool.     Explain 
what  happens. 

When  a  substance  consisting  of  carbon  and  hydrogen 
burns  in  chlorin  what  is  the  chemical  action?  Compare 
combustion  in  air  with  combustion  in  chlorin. 

Is  chlorin  an  element  that  is  very  active  chemi- 
cally? 

EXP.  31.    BLEACHING   WITH   HYPOCHLOROUS    ACID,  HC10 

Materials.  Calcium  hypochlorite  (contained  in  "  bleach- 
ing powder  "  or  "  chloride  of  lime  ").  Hydrochloric  acid, 
HC1.  Potassium  carbonate  (K2CO3)  solution.  Litmus 
solution.  Indigo  solution.  A  bottle  of  dry  chlorin. 
Pieces  of  calico  or  other  colored  cotton  cloth. 

Apparatus.  Funnel  and  ring  stand.  Beakers.  Watch 
glasses  or  evaporating  dishes. 


EXPERIMENTS  61 

Procedure. 

1.  Notice   the   odor   of   fresh   bleaching   powder.     Oi 
what  does  it  remind  you  ? 

2.  Mix  10  g.  of  bleaching  powder  with  150  ccm.  of 
water.     In  a  short  time  filter  the  resulting  liquid,  and 
notice    the    odor   of   the   filtrate.      Is   bleaching   powder 
soluble  in  water  ? 

3.  To  5  ccm.  of  the  solution  on  a  watch  glass  add  a 
few  drops  of  HC1.     Judging  by  the  odor,  what  gas  is 
liberated?     What     can     you    say     of    the    stability    of 
hypochlorous  acid? 

4.  To  10  ccm.  of  the  bleaching  powder  solution  add 
a  drop  or  two  of  litmus  solution.     Make  a  similar  test 
with  indigo  solution  and  with  bits  of  the  colored  cloth. 
Allow  to  stand  if  no  result  appears  at  first. 

Make  similar  tests  with  the  bleaching  powder  solution 
to  which  a  little  HC1  has  been  added.  Is  the  action 
quicker  with  or  without  the  acid  ?  Why  ? 

5.  To    20    ccm.    of    bleaching    powder    solution    add 
potassium    carbonate     solution    until    a    precipitate    no 
longer     forms.      Filter     off     the     precipitated     calcium 
carbonate.     The  resulting  solution,  often  called  Javelle 
water,  contains  potassium  hypochlorite  and  is  frequently 
used  in  the  home  to  remove  stains.      Test  its  power  to 
bleach  colored  cloth,  with  and  without  the  assistance  of 
hydrochloric    acid.     Why    do    directions    for    home    use 
often  say  to  add  vinegar  to  the  Javelle  water  ? 

Write  an  equation  indicating  the  formation  of  potassium 
hypochlorite. 

Test  similarly  the  solution  in  the  beaker  into  which  the 
exit  tube  of  the  chorin  generator  dipped  in  the  last  experi- 
ment. Does  it  seem  to  be  identical  with  Javelle  water  ? 
From  what  was  it  formed  ?  Write  an  equation  showing  the 
reaction,  consulting,  if  necessary,  the  reaction  given  below. 


62 


LABORATORY  MANUAL  IN  CHEMISTRY 


6.  Into  the  bottle  of  dry  cblorin  introduce  a  piece 
of  moist  colored  cloth  and  a  similar  piece  that  is 
thoroughly  dry.  Do  not  allow  the  two  to  come  in 
contact.  Which  piece  is  bleached  more  rapidly?  See 
whether  pure  water  will  bleach  another  piece  of  the 
cloth.  Judging  from  the  effect  on  the  dyed  cloth,  what 
seems  to  be  formed  when  chlorin  and  water  are  brought 
together?  The  equation  expressing  the  reaction  of 
chloriri  and  water  is 

2  Cl  4-  H2O  ->  HC1  +  HOC1 

What  industrial  use  for  chlorin  and  hypochlorous  acid 
do  you  know  of  ? 

EXP.  32.    THE  PERCENTAGE  OF  OXYGEN  IN  POTASSIUM 

CHLORATE 

THE  WEIGHT  OF  ONE  LITER  OF  OXYGEN 

Materials.      Potassium    chlorate,   KC1O3,   dried    on   a 

radiator  or  in  an  oven. 

Apparatus  as  shown  in  Fig.  21.     A  is  a  test  tube   of 

hard  glass,  connected  by  a  one-holed  rubber  stopper  and 

a  delivery  tube  to  the  liter 
bottle  B.  It  is  fitted  with  a 
tight  rubber  stopper  pierced 
with  two  holes.  Through 
one  hole  passes  the  tube  lead- 
ing from  A.  Through  the 
other  hole  passes  a  tube,  D, 
shaped  like  an  inverted  U,  one 
arm  of  which  reaches  to  the 

bottom  of  B.      C  is  a  500  ccm.  beaker.     Barometer  arid 

thermometer  for  general  class  use. 

Procedure.     Set   up   the    apparatus  as   shown  and   see 

that  all  joints  are   tight  by  sucking  on   the   end  of  the 


FIG.  21. 


EXPERIMENTS  63 

U-shaped  tube ;  then  remove  the  test  tube  and  weigh  it 
carefully  on  a  delicate  balance.  Into  the  tube  put  1-1.5 
g.  of  potassium  chlorate.  Jar  the  tube  so  that  the  potas- 
sium chlorate  collects  at  the  closed  end,  and  then  weigh 
again.  Weigh  the  500  ccm.  beaker  to  a  tenth  of  a  gram 
on  a  platform  scale.  Fill  the  bottle  nearly  full  of  water 
and  cause  the  tube  D  to  fill  with  water  by  blowing  gently 
into  the  delivery  tube  leading  from  A  and  plug  the  end 
of  the  U-tube  with  a  squill  of  filter  paper.  Insert  the 
stopper  and  delivery  tube  tightly  into  the  test  tube  con- 
taining the  potassium  chlorate.  Remove  plug  from  U- 
tube  and  place  weighed  beaker  under  the  open  end. 

Heat  the  tube  A  in  the  flame  of  the  burner  until  no 
further  change  in  its  contents  takes  place.  Move  the 
burner  back  and  forth  at  first  so  as  to  make  a  gentle  heat, 
but  afterwards  make  it  intense  enough  to  decompose  all 
of  the  potassium  chlorate.  If  the  molten  mass  froths  and 
leaves  a  deposit  high  up  in  the  tube,  heat  this  deposit 
until  it  melts  and  runs  back  to  the  bottom. 

When  all  the  oxygen  has  been  driven  off  and  only 
molten  potassium  chlorid  remains  in  the  tube  A,  allow  it 
to  cool.  Raise  or  lower  the  beaker  so  that  the  inverted 
U-tube  dips  as  far  into  the  water  in  the  beaker  as  it  does 
into  the  water  in  the  bottle.  Then  remove  the  beaker 
and  the  test  tube  in  the  order  named  and  weigh  the  test 
tube  again  on  the  delicate  balance.  Take  the  tempera- 
ture of  the  water  as  that  of  the  gas  and  note  the 
barometric  pressure.  Tabulate  results  thus  °. 

Weight  of  tube  and  potassium  chlorate 

Weight  of  tube  empty 

(a)   Weight  of  potassium  chlorate  taken     .... 

Weight  of  tube  and  potassium  chlorate 

Weight  of  tube  and  potassium  chlorid 

( 6)   Weight  of  oxygen  lost t 


64          LABORATORY  MANUAL  IN  CHEMISTRY 

(<?)  Find  how  much  oxygen  would  be  obtained  from 
1  g.  of  potassium  chlorate  thus : 

The  weighed  amount  1      ("the  weight  of  1       fl  g.  of  potas-1      f       ofoxv- 
of  potassium  chlo-  I  :  \     oxygen         I  ::  j      siuni  chlo-  I  :  | 
rate  (a)  J      [     lost  (6)       J       [    rate  J      [ 

What  is  the  percentage  of  oxygen  in  potassium 
chlorate  ? 

(d)  Figure  out  the  weight  of  potassium  chlorid  left  in 
the  tube  and  calculate  how  much  is  formed  from  1  g.  of 
potassium  chlorate. 

(e)  Weigh  the  beaker  and  the  water  it  contains  to  the 
tenth  of  a  gram  and  calculate  the  volume  of  water  in  the 
beaker,  remembering  that  1  ccm.  weighs  1  g.     The  vol- 
ume of  the  water  is  the  same  as  the  volume  of  the  oxy- 
gen  evolved.       Why?      Subtract    the    pressure   due   to 
water  vapor   (see  text,  p.  410)  from  the  barometric  read- 
ing to  get  the  pressure  of  the  oxygen,  and  reduce  the 
volume  to  standard  conditions. 

What  is  the  weight  of  this  volume  of  oxygen  ? 

Then,  if  the  volume  of  oxygen  in  cubic  centimeters  has 
the  weight  in  grams  just  recorded,  1000  ccm.  (1  1.)  of 
oxygen  has  a  weight  that  is  in  the  same  ratio.  Calcu- 
late thus  the  weight  of  1  1.  of  oxygen  under  standard 
conditions. 

NOTE.  The  instructor  should  average  the  results  of  the  whole 
class,  and  should  explain  why  the  average  result  of  careful  work 
should  be  more  nearly  correct  than  most  single  experiments.  He 
should  also  call  attention  to  the  way  in  which  one  careless  bit  of 
work  may  affect  the  results  of  a  series  of  painstaking  experiments. 


EXPERIMENTS 


65 


EXP.  33.     DETERMINATION  OF   THE    VOLUME   RATIO  IN 
WHICH  HYDROGEN  AND  OXYGEN   COMBINE 

Instructor's  Experiment 

Material.     Mercury. 

Apparatus.  A  eudiometer,  coil,  dry  battery,  beaker, 
and  standard,  as  shown  in  Fig.  22.  A  hydrogen  gener- 
ator and  oxygen  generator,  or 
better  hydrogen  and  oxygen 
drawn  from  gas  holders.  A 
cork  to  fit  the  eudiometer. 

Procedure.  Set  up  the  ap- 
paratus as  shown  and  fill  the 
eudiometer  completely,  even 
the  tip  of  the  tube  above  the 
stopcock,  with  mercury.  In- 
troduce into  the  eudiometer 
about  20  ccm.  of  pure  hy- 
drogen, taking  care  that  the 
tubes  leading  from  the  gen- 
erator or  gas  holder  are  full 
of  hydrogen  (not  of  air)  be- 
fore connecting  with  the  tube 
above  the  stopcock.  In  order 
that  gas  may  enter  the  apparatus  it  will  be  necessary  to 
draw  off  some  mercury  into  the  beaker.  When  approxi- 
mately 20  ccm.  have  entered,  shut  the  stopcock  and  make 
the  level  the  same  in  both  arms  by  drawing  off  or  adding 
mercury  to  the  tube  B.  Measure  the  volume  of  hydrogen 
in  the  graduated  tube  A.  After  the  volume  of  hydrogen 
has  been  noted,  introduce  about  the  same  volume  of  oxy- 
gen, observing  all  the  directions  given  for  hydrogen. 
Note  the  volume  of  oxygen  added. 

Pour  mercury  into  B  until  a  quantity  is  present  greater 


FIG.  22. 


66         LABORATORY  MANUAL  IN  CHEMISTRY 

than  is  necessary  to  fill  completely  one  side  of  the 
apparatus,  and  press  a  cork  into  the  open  end  of  the  tube 
B.  Connect  the  wires  fused  in  the  top  of  the  tube  A 
with  the  coil  and  pass  a  spark  through  the  mixed  gases. 
What  happens  ?  Write  an  equation  representing  the 
reaction  which  takes  place. 

Remove  the  cork  from  B.     Explain  what  happens  ? 

The  amount  of  water  formed  in  the  reaction  condenses 
and  occupies  no  volume  worth  consideration.  Pour 
mercury  into  B  until  the  level  is  the  same  in  both  sides 
of  the  apparatus,  and  measure  the  volume  of  the  remain- 
ing gas,  which  in  the  present  instance  is  oxygen,  as  may 
be  proven  by  testing  its  effect  on  a  glowing  splint.  Re- 
cord your  results  as  follows  and  calculate  the  volume 
ratio  in  which  hydrogen  and  oxygen  combine. 

ccm.  volume  of  hydrogen,  ccm.  volume  of  oxygen  introduced, 

ccm.  volume  of  oxygen,  ccm.  volume  of  oxygen  left  over, 

ccm.  total  volume,  •        ccrn.  volume  of  oxygen  used. 

ccm.  of  hydrogen  gas  unite  with        ccm.  of  oxygen  gas  to  form 
water.     The  ratio  is       :      : 

Repeat  the  experiment,  using  about  30  ccm,  of  hydrogen 
and  10  ccm.  of  oxygen  in  order  to  show  that  it  makes  no 
difference  which  element  is  present  in  excess.  Avoid 
using  the  exact  ratio  of  2:1,  lest  the  violence  of  the 
explosion  wreck  the  apparatus.  Results  varying  from 
the  correct  ratio  are  caused  usually  by  the  inclusion  of 
some  air  during  the  manipulation,  or  by  impure  gases. 

EXP.  34.    BASES 

Materials.  Solutions  of  sodium  hydroxid,  NaOH  (89  g. 
in  1  1.  of  solution)  ;  of  hydrochloric  acid  (165  ccm.  of 
cone.  HC1  in  1  1.  of  solution)  ;  of  copper  sulfate,  CuSO4 ; 
of  ferric  chlorid,  FeCl3 ;  and  of  magnesium  sulfate. 


EXPERIMENTS  67 

MgSO4.  Sodium.  Lime  (calcium  oxid),  CaO.  Litmus 
paper.  A  solution  of  1  g.  of  phenolphthalein  in  100  ccm. 
of  dilute  alcohol  (half  water). 

Apparatus.  Beakers.  Stirring  rods.  Test  tubes.  Evap- 
orating dishes. 

Procedure,     (#)  Methods  of  formation. 

1.  Action  of  strong  metals  on  water. 

Remove  the  oil  from  a  piece  of  sodium  about  as  large  as 
a  pea  by  pressing  between  filter  papers.  Throw  it  into 
an  evaporating  dish  half  full  of  water,  watching  the  action 
through  a  piece  of  glass  or  standing  at  some  distance  to 
avoid  being  hit  by  spattering  drops.  What  happens? 
When  the  action  is  over  try  the  effect  of  the  solution  on 
the  fingers.  Touch  a  finger  to  the  tongue.  What  is  its 
taste  ?  What  is  its  effect  on  pieces  of  red  and  blue  litmus 
paper?  Add  a  few  drops  of  phenolphthalein  solution. 
What  happens  ? 

The  substance  contained  in  the  water  is  sodium  hy- 
droxid.  It  is  a  typical  strong  base  or  alkali.  Write  an 
equation  indicating  its  formation  from  sodium  and  water. 

2.  Action  of  the  oxids  of  some  metals  on  water. 
Place  a  piece  of  lime  as  big  as  a  hazelnut  in  a  small 

beaker  and  pour  upon  it  about  5  ccm.  of  water.  What 
happens  after  standing  10  minutes  or  less  ?  The  substance 
formed  is  calcium  hydroxid,  Ca(OH)2.  Write  an  equation 
showing  how  it  is  formed  from  calcium  oxid  and  water. 
Put  some  of  the  resulting  substance  in  a  test  tube  of 
water,  shake  thoroughly  and  allow  to  settle.  Decant  the 
clear  liquid  and  test  as  you  did  the  sodium  hydroxid  in 
(1).  Is  calcium  hydroxid  a  strong  base  ? 

3.  Insoluble  bases  by  precipitation. 

Place  2-3  ccm.  of  copper  sulfate,  ferric  chlorid,  and 
magnesium  sulfate  in  separate  test  tubes  and  dilute  each 


68          LABORATORY  MANUAL  IN   CHEMISTRY 

to  10  com.  with  water.  Add  a  few  drops  of  sodium  hy- 
droxid  to  each  solution  and  note  the  precipitation  of  the 
insoluble  bases,  Cu(OH)2,  Fe(OH)3,  and  Mg(OH)2. 
Write  equations  for  their  formation.  Do  the  reactions 
run  to  equilibrium  or  to  completion  ?  Why  ? 

Insoluble  bases  have  no  taste  and  no  effect  on  the  fingers 
or  on  indicators  that  is  appreciable.  They  react  with  acids, 
however,  just  as  soluble  bases  do. 

(£>)  Neutralization. 

Place  20  ccm.  of  NaOH  solution  in  a  beaker,  add  a  few 
drops  of  phenolphthalein,  and  add,  with  stirring,  HC1  until 
the  color  just  disappears.  To  be  sure  that  no  excess  of 
acid  is  present,  add  NaOH  drop  by  drop  until  the  pink 
color  reappears,  then  finally  bleach  with  a  single  drop 
of  acid. 

Dip  the  fingers  into  the  resulting  solution,  taste  and 
smell  it.  Can  you  detect  either  base  or  acid  ?  To  be  sure 
that  the  solution  is  not  merely  a  mixture  in  which  the 
properties  of  the  acid  hide  those  of  the  base,  and  vice 
versa^  evaporate  the  solution  to  dry  ness  and  taste  the  solid 
left.  What  is  it?  Has  a  new  substance  been  formed? 
To  what  class  of  substances  does  it  belong?  Write  an 
equation  expressing  its  formation. 

(<?)  Methods  offoming  salts. 

The  several  methods  of  forming  salts  illustrated  in  the 
laboratory  work  so  far  may  be  summarized  as  follows : 

1.  By  the  interaction  of  elements,  as on 

2.  By  the  action  of  acids  on  metals,  as on 

3.  By  the  action  of  acids  on  oxids,  as on 

4.  By  the  action  of  acids  on  bases,  as on 

5.  By  metathesis  when  there  is  formed 

(a)  a  gaseous  substance,  as on 

(5)  an  insoluble  substance,  as on  — 


EXPERIMENTS  69 


EXP    35.     NITROGEN  — ITS   PREPARATION  AND 
PROPERTIES 

Instructor's  Experiment 

Materials.  Yellow  phosphorus.  Sodium  nitrite,  NaNO2, 
or  potassium  nitrite,  KNO2.  Ammonium  chlorid,  NH4C1. 

Apparatus.  A  tin  box-cover  or  some  similar  object  that 
will  float  on  water.  A  stoppered  bell  jar  or  a  two-liter 
bottle  cut  off  near  the  bottom  and  fitted  with  a  stopper. 
A  pneumatic  trough.  Apparatus  as  shown  in  Fig.  23, 
consisting  of  a  half-liter  flask  fitted  with  a  two-hole 
stopper  through  which  pass  a  small  separating  funnel  * 
arid  exit  tube  as  shown.  Ring  stand  and  gauze.  5-6 
fruit  jars  or  bottles.  Combustion  spoon. 

Procedure,     (a)  Natural  nitrogen  from  air. 

Float  the  cover  hollow  side  up  on  water  in  a  tank. 
Place  in  it  a  piece  of  phosphorus  the  size  of  a  pea  and 
light  the  phosphorus.  Quickly  cover  the  burning  phos- 
phorus with  the  bottle,  pressing  the  bottle  down  into  the 
water  so  that  air  is  imprisoned  inside  the  bottle  over  the 
water.  Describe  and  explain  what  happens.  What  is 
the  "  smoke  "  ?  What  constituent  of  the  atmosphere  is 
used  up  ?  The  remaining  gas  is  mostly  nitrogen. 

Allow  the  bottle  to  stand  until  the  "smoke"  has  dis- 
solved in  the  water  and  the  gas  in  the  bottle  is  clear  ; 
then  make  the  water  level  the  same  inside  and  outside  the 
bottle.  The  nitrogen  in  the  bottle  is  sufficiently  pure  for 
most  experiments.  Does  it  have  any  color,  odor,  or  taste  ? 
Determine  by  proper  experiments  whether  nitrogen  burns 
or  supports  combustion. 

*  A  thistle  tube  will  serve  the  purpose  if  a  separating  funnel  is  not 
available. 


70 


LABORATORY  MANUAL  IN   CHEMISTRY 


FIG.  23. 


(5)    Chemically  pure  nitrogen. 

Set  up  the  apparatus  as  shown  in  Fig.  23.  Dissolve 
16  g.  of  ammonium  chlorid  in  50  ccm.  of  water  and  intro- 
duce the  solution  into  the 
flask  through  the  separat- 
ing funnel.  Dissolve  20 
g.  of  sodium  nitrite  or  25 
g.  of  potassium  nitrite  in 
25  ccm.  of  water  and  put 
the  solution  into  the  sepa- 
rating funnel.  Allow  5 
ccm.  of  the  nitrite  solution 
to  run  into  the  flask,  then 
close  the  stopcock.  Heat 
the  mixture  with  a  burner, 
so  regulating  the  heating 
that  the  liberation  of  gas  does  not  become  too  rapid.  If 
the  action  slackens,  add  more  nitrite  solution,  a  few  cubic 
centimeters  at  a  time.  When  the  air  has  been  driven  out 
of  the  apparatus  collect  several  bottles  of  gas. 

Determine  by  proper  experiments  whether  this  gas  — 
pure  nitrogen  —  has  color,  odor,  or  taste  ;  whether  it 
burns  or  supports  combustion.  Ignite  a  piece  of  phos- 
phorus in  a  combustion  spoon  and  put  it  into  a  bottle  of 
gas,  replacing  the  cover  to  prevent  the  rapid  escape  of 
nitrogen.  What  happens  ?  Does  the  gas  seem  to  have 
the  same  properties  as  that  prepared  in  (a)?  Does 
nitrogen  seem  to  be  an  inert  or  an  active  gas  ? 

The  liberation  of  nitrogen  is  due  to  the  decomposition 
of  ammonium  nitrite,  formed  by  metathesis  from  the  re- 
agents used.  Water  is  another  decomposition  product. 
Write  equations  expressing  the  formation  and  decomposi- 
tion of  ammonium  nitrite.  What  substance  remains  dis« 
solved  in  the  liquid  in  the  flask  ? 


EXPERIMENTS 


71 


EXP.  36.     NITRIC  ACID 

Materials.  Sodium  nitrate,  NaNO3.  Cone.  H2SO4. 
A  cone,  solution  of  ferrous  sulfate,  FeSO4.  Wooden 
splints.  Small  pieces  of  iron  and  zinc.  Hair  or  wool. 

Apparatus.  A  small  glass  retort.  A  flask  into  which 
the  neck  of  the  retort  fits.  Ring  stand.  A  glass  tube. 
Test  tubes  and  a  beaker.  A  dish  or  beaker  full  of  water. 

CAUTION  :  Do  not  allow  nitric  acid  to  come  into  con- 
tact with  the  skin  or  the  clothes. 

Procedure,     (a)  Preparation. 

Place  30  g.  of  sodium  nitrate  in  the  retort,  and  set  up 
the  apparatus  as  shown  in  Fig.  24,  Remove  the  stopper 
from  the  retort,  pour  in  20  ccm. 
of  cone.  H2SO4  by  means  of  a 
funnel  and  replace  the  stopper. 
Heat  the  contents  of  the  retort 
gently,  so  that  a  liquid  distills 
over  into  the  flask.  If  the  latter 
becomes  hot,  rotate  it  in  the 
dish  of  water  to  keep  it  cool. 
Continue  the  heating  with  a 
small  flame  until  no  more  nitric 
acid  passes  into  the  receiver. 
Why  does  the  nitric  acid  cease 
to  distill  ?  Does  the  reaction  in  the  retort  run  to  equilib- 
rium or  to  completion  ?  Why  ?  Write  the  equation  for 
the  reaction.  Consult  the  text  and  find  two  reasons  why 
HC1  could  not  be  used  in  place  of  H2SO4  in  making 
HNO3.  When  cold,  extract  contents  of  retort  with  water. 

(5)  Properties. 

1.  Notice  the  color  of  the  nitric  acid;  the  yellowish 
tint  is  caused  by  gaseous  impurities  dissolved  in  the  liquid. 


FIG.  24. 


72          LABORATORY  MANUAL  IN   CHEMISTRY 

Pat  a  few  ccm.  of  HNO3  in  a  test  tube,  and  heat  to  boiling. 
What  colored  gas  is  given  off  at  first  ?  What  is  the  color 
of  the  vapor  of  HNO3  later?  What  is  the  color  of  the 
HNO3  left  in  the  test  tube  ? 

2.  Keep  some  HNOg  boiling  in  a  test  tube  and  introduce 
into  the  fumes  a  glowing  spark  on  the  end  of  a  long  wooden 
splint.     Does  it  continue  to  burn  ?     What  makes  wood 
burn  ?     Where  does  the  wood  get  this  substance  ?     A  de- 
composition  product  of   HNO3  may  be  seen  in  the  test 
tube  above  the  glowing  spark.    What  is  its  color  ?    Where 
did  you  see  it  before  ?     Note  color  given  to  the  uncharred 
wood  by  the  HNO3. 

3.  Boil  some  HNO3  in  a  test  tube  in  the  mouth  of  which 
is  placed  a  loosely  fitting  plug  of  hair  or  wool.     (Hood.) 
What  happens  ?     From  the  last  two  tests  what  conclusions 
do  you  draw  as  to  the  oxidizing  action  of  HNO3? 

4.  Pour  some  HNO3  upon  bits  of  iron  and  zinc  in  sepa- 
rate test  tubes.     Compare  the  action  with  that  of  HC1  on 
these  same  metals. 

5.  To  5  ccm.  of  a  cone,  solution  of  ferrous  sulfate,  add 
a  minute    crystal  of   sodium   nitrate   and    shake  to  mix 
thoroughly.     Hold  the  test  tube  in  an  inclined  position 
and  pour  down  the  side  of  the  test  tube  about  5  ccm.  of 
cone.  H2SO4  so  that  it  will  underlie  the  solution  without 
mixing.     Note  the  formation  of  the  dark  ring  on  the  line 
of  contact.    This  procedure  is  used  as  a  test  for  nitrates,  for 
any  other  nitrate  will  give  the  same  reaction. 

EXP.  37.    NITROGEN  MONOXID,  OR  NITROUS  OXID,  N20 

Materials.  Ammonium  nitrate,  NH4NO3.  Phosphorus. 
Wooden  splints.  Cobalt  chlorid  solution. 

Apparatus  as  shown  in  Fig.  25.  A  large  beaker  of 
about  1  1.  capacity.  Three  bottles.  Combustion  spoon. 


EXPERIMENTS 


73 


FIG.  25. 


While  setting  up  the  apparatus,  place  the  large  beaker 
full  of  water  on  a  gauze  over  a  burner  and  heat  for  use  later. 

Procedure,      (a)   Preparation. 

Place  about  15  g.  of  ammonium  nitrate  in  the  test  tube 
and  set  up  the  apparatus  as  shown  in  Fig,,  25.  Heat 
gently  until  the  ammo- 
nium nitrate  melts  and 
gas  is  evolved,  but  do 
not  cause  the  reaction 
to  go  too  rapidly  by 
overheating.  Fill  the 
bottles  in  which  the  gas 
is  to  be  collected  with 
warm  water  and  collect 
three  bottles  of  the  gas. 

The  gas  liberated  is  nitrogen  monoxid,  often  called 
44  laughing  gas."  Test  the  liquid  that  condenses  in  the 
side-neck  test  tube  and  see  if  it  is  water.  Write  the 
equation  expressing  the  reaction  taking  place.  How  does 
it  differ  from  the  similar  reaction  used  to  prepare  nitrogen 
(Exp.  35  5)  ? 

(5)  Properties. 

1.  Note  the  color,  odor  and  taste  of  the  gas.     Fill  a 
test  tube  with  the  gas  by  downward  displacement,  close 
with  the  thumb  and  invert  in  a  dish  of  water.     What 
happens  ?     Why  use  hot  water  in  collecting  the  gas  ? 

2.  Insert  a  burning   splint   into  a  bottle  of   the  gas. 
Does  nitrogen  monoxid  burn  or  support  combustion  ? 

3.  Place  a  piece  of  phosphorus  in  a  combustion  spoon, 
ignite  and  insert  in  a  bottle  of  the  gas.     What  happens  ? 

Nitrogen  monoxid  is  decomposed  into  its  elements  at  the 
temperature  of  burning  wood  or  phosphorus.  On  this 


74          LABORATORY  MANUAL   IN   CHEMISTRY 

basis  explain  why  these  substances  should  burn  better  in 
this  gas  than  in  air. 

EXP.  38.    NITROGEN  DIOXID,  OR  NITRIC  OXID,  N203 

Materials.  Copper.  Cone,  nitric  acid,  IINO3.  Phos- 
phorus. Wooden  splints.  Oxone  (fused  sodium  peroxid), 
Na202. 

Apparatus.  Same  as  for  making  hydrogen,  Fig.  13. 
Bottles.  Combustion  spoon.  Small  oxygen  generator 
consisting  of  a  side-neck  test  tube  and  medicine  dropper 
as  shown  in  Fig.  26. 

Procedure,     (a)  Preparation. 

Place  about  20  g.  of  copper  in  the  bottle,  insert  the 
stopper  and  through  the  thistle  tube  add  about  20  com. 
of  water  and  10  ccm.  of  cone.  HNO3.  Action  will  begin 
at  once,  but  additions  of  HNO3  will  be  required  later. 

Collect  three  or  four  bottles  of  gas  by  displacement  of 
water. 

(5)  Properties. 

1.  Note  the  color  of  the  gas  that  first  fills  the  genera- 
tor.    After  it  has  bubbled  through   the  water,  note  the 
color  of  the  nitrogen  dioxid  that  collects  in  the  bottles. 
What  must  have  become  of  the  brown  gas  ? 

Remove  the  cover  from  a  bottle  of  nitrogen  dioxid  and 
expose  it  to  the  air.  What  happens  ?  How  was  the 
brown  gas  formed  that  first  filled  the  generator  ? 

2.  To   ascertain  which  constituent  of   the   air   causes 
nitrogen  dioxid  to  turn  brown,  collect  a  half  bottle  of  gas 
from  the  generator.     Place  a  piece  of  oxone  as  big  as  a 
hazelnut  in  the  little  oxygen  generator  shown  in  Fig.  26. 
Fill  the  medicine  dropper  with  water,  insert  the  stopper 
and  by  gently  squeezing  let  a  couple  of  drops  of  water  fall 


EXPERIMENTS  75 

on  the  oxone.     This  generates  oxygen  according  to  the 
equations  : 

2  H20  ->  2  NaOH  +  H2O2 


Fill  the  other  half  of  the  bottle  containing  nitrogen  dioxid 
with  oxygen.     What  happens?     The  brown  gas  is  nitro 
gen  tetroxid,  N2O4.     What  constituent  of  the 
air  is  it  that  causes  nitrogen  dioxid  to  turn 
brown  ? 

3.  Insert  a  burning  splint  into  a  jar  of 
gas,  removing  the  cover  only  as  little  as  is 
necessary.  Does  nitrogen  ,  dioxid  burn  or 
support  combustion  ? 

Place  a  piece  of  phosphorus  in  a  combus- 
tion spoon,  ignite  and  insert  in  a  bottle  of 
nitrogen  dioxid.  What  happens  ? 

Nitrogen  dioxid  is  decomposed  into  its  elements  at  the 
temperature  produced  by  burning  phosphorus,  but  not  at 
the  temperature  of  a  burning  splint.  Explain  the  pre- 
ceding results  on  this  basis. 

(c)   The  reactions. 

Several  different  reactions  take  place  at  the  same  time 
when  nitric  acid  acts  on  copper.  The  metal  is  oxidized 
by  nitric  acid  to  the  oxid  which  then  dissolves  in  more 
acid  to  form  a  salt  as  the  equations  show. 

2  HNO3  ->  H2O  +  N2O2  +  —  O 

3Cu  +  ----  >  - 


3 +  —  HNO3  ->  3  Cu(NO3)2  +  - 

What  colors  the  liquid  in  the  generator  blue  ? 


76 


LABORATORY  MANUAL  IN  CHEMISTRY 


EXP.  39.  AMMONIA,  NH3 

Materials.  Ammonium  chlorid,  NH4C1.  Freshly 
slaked  lime  (calcium  hydroxid)  Ca(OH)2.  Cone.  HC1. 
Litmus  paper.  Wooden  splint. 

Apparatus.     As  shown  in  Fig.  27.     Three  bottles. 

Procedure,     (#)  Preparation. 

Take  a  quarter  of  a  test  tube  full  of  ammonium  chlorid 
and  the  same  amount  of  calcium  hydroxid.  Smell  of  each 
and  note  whether  either  has  an  odor.  Mix  the  two  sub- 
stances thoroughly  on  a  paper  and  cautiously  smell  again. 
What  is  the  odor  ?  How  could  it  have  been  produced  ? 
What  would  be  the  effect  of  raising  the  temperature? 
Complete  the  equation 

Ca(OH)2  +  2  NH4C1  ->  CaCl2  + + 

Put  the  mixture  into  the  test  tube  and  set  up  the  ap- 
paratus as  shown  in  Fig.  27  and  heat  gently.  Turn  the 
outlet  tube  up  and  collect  a  bottle 
full  of  gas  by  upward  displacement  as 
shown  by  the  dotted  lines.  What 
does  this  indicate  as  to  the  relative 
density  of  air  and  ammonia? 


(#)  Properties. 

1.  Hold  a  moistened  finger  in  the 
gas  and  touch  to  the  tongue.     What 
is  the  taste  of  ammonia  ? 

2.  Thrust  a  lighted  wooden  splint 
up  into  the  bottle  of  ammonia.     Does  it  burn  or  support 
combustion  ? 

3.    Put  3-4  drops  of  cone.  HC1  in  a  bottle,  cover  with 
a  glass  and  shake  thoroughly.     Lift  the  bottle  containing 


FIG.  27. 


EXPERIMENTS  77 

NHg  from  over  the  outlet  tube  of  the  generator,  cover 
with  a  glass  plate  and  then  place  mouth  upward  on  the 
table.  Place  the  bottle  containing  the  HC1  mouth  down- 
ward over  the  bottle  containing  the  N  H3  and  remove  both 
glass  plates.  Note  what  happens.  Stand  the  bottles 
aside  in  order  that  the  substance  may  settle.  After  it 
has  settled  remove  the  upper  bottle  and  allow  any  am- 
monia to  escape. 

4.  Collect  some  ammonia  in  a  test  tube  by  upward  dis- 
placement, cover  with  the  thumb  and  invert  in  a  pan  of 
water.  Remove  thumb  and  explain  results.  Why  not 
collect  ammonia  over  water  ? 

(c)  Ammonium  hydroxid,  NH4OH. 

Turn  the  outlet  tube  of  the  generator  down  and  insert 
it  in  a  bottle  containing  about  20  com.  of  water,  keeping 
the  end  of  the  tube  just  above  the  surface  of  the  water  as 
shown  in  Fig.  27.  Why  not  dip  it  into  the  water? 
Shake  the  bottle  occasionally  to  mix  the  liquid  thoroughly 
and  continue  the  reaction  as  long  as  the  gas  is  readily 
absorbed  by  the  water.  Satisfy  yourself  that  the  liquid 
in  the  bottle  is  identical  with  the  ammonium  hydroxid 
of  the  laboratory  by  noting  the  odor  and  effect  on  red 
litmus  paper  of  each  solution.  A  reaction  must  have 
taken  place  between  the  gas  and  the  water.  Complete 
the  equation 

_  +  _     -- 


1.  Heat  in  a  test  tube  about  10  ccm.  of  the  solution 
in  the  bottle,  noting  by  the  odor  what  comes  off   first. 
Continue   the   heating  until  about  half  of   the  liquid  is 
boiled    away.       Can    you    now    detect    any    ammonia? 
What  must  have  happened  to  the  ammonium  hydroxid  ? 
Is  the  reaction  written  above  reversible  or  not  ? 

2.  Add  dilute  HC1  to  the  remainder  of  the  liquid  in 


78         LABORATORY  MANUAL   IN   CHEMISTRY 

the  bottle  until  it  will  just  turn  blue  litmus  paper  red. 
Evaporate  to  dryness  and  compare  the  product  obtained 
with  that  formed  in  (5)  3,  as  to  taste,  odor,  effect  of  heat, 
and  of  sodium  hydroxid  upon  each.  The  substance  is  in 
each  case  ammonium  chlorid,  NH4C1.  Write  equations 
expressing  its  formation  in  each  case. 

3.  Any  ammonium  salt  heated  with  a  strong  base,  such 
as  NaOH,  KOH  or  Ca(OH)2,  will  liberate  ammonia,  which 
may  be  detected  by  the  odor  or  by  red  litmus  paper.  This 
is  a  test  for  ammonium  salts. 

EXP.  40.    DECOMPOSITION  OF  AMMONIA  BY  ELECTRICITY 

Instructor's  Experiment 

Materials.  Cone,  ammonia  water  (ammonium  hy- 
droxid), NH4OH.  Salt.  Wooden  splints. 

Apparatus.  Same  as  used  in  the  decomposition  of 
water  by  electricity,  Fig.  11. 

Procedure.  Into  the  bowl  of  the  apparatus  place  a  suf- 
ficient quantity  of  a  mixture  of  cone,  ammonium  hydroxid 
and  water  (equal  volumes)  to  cover  the  electrodes  and 
dissolve  in  the  mixture  about  25  g.  of  salt.  Fill  the 
graduated  test  tubes  or  measuring  glasses  with  the  solu- 
tion and  invert  over  the  electrodes.  Connect  the  wires 
to  a  dynamo  or  battery  and  note  the  evolution  of  gas. 
At  what  rate  does  it  collect  in  each  test  tube  ?  When 
one  of  the  tubes  is  full  of  gas  remove  it  from  the  bowl 
and  holding  it  mouth  down  thrust  up  into  it  a  lighted 
wooden  splint.  What  gas  does  it  contain  ? 

When  the  other  tube  is  full  of  gas,  test  it  similarly. 
What  happens?  This  gas  is  nitrogen. 

How  many  volumes  of  hydrogen  combine  with  one  vol- 
ume of  nitrogen  to  form  ammonia  ? 

NOTE.  The  reaction  which  takes  place  is  not  as  simple  as  it  ap- 
pears. Investigation  shows  that  it  is  the  salt  which  is  decomposed 


EXPERIMENTS  79 

by  the  electric  current,  sodium  being  liberated  at  the  cathode  and 
chlorin  at  the  anode.  Consult  Exp.  16  (7;)  and  explain  why  hydrogen 
is  collected  at  the  cathode  in  this  experiment.  Recalling  the  action 
of  chlorin  on  compounds  containing  hydrogen  (see  Exp.  30  (c)),  ex- 
plain why  nitrogen  collects  at  the  anode.  What  other  product  is 
formed  by  the  sodium  ;  by  the  chlorin  ?  What  becomes  of  these  two 
products  when  they  come  together  in  the  solution?  What  then  is  the 
action  of  the  salt  in  the  present  experiment?  Write  equations  for 
all  the  reactions  involved. 

EXP.  41.    THE  EQUIVALENT  OF  MAGNESIUM 

Materials.     Cone.  HC1.     Magnesium  ribbon. 

Apparatus.  As  shown  in  Fig.  28  consisting  of  a  half 
liter  flask,  small  evaporating  dish  and  pan  of  water.  Stiff 
card  or  small  square  of  glass.  Gradu- 
ate, thermometer,  and  barometer  for 
general  class  use. 

Procedure.  Weigh  accurately  not 
more  than  0.5  g.  of  magnesium  ribbon.* 
Roll  or  tie  it  into  a  little  ball  that  will 
readily  slip  into  the  neck  of  the  flask. 
Place  the  ball  of  magnesium  in  the  dish 
and  the  dish  in  the  pan  containing  suf- 
ficient water  to  cover  the  dish  to  a  depth  of  3  to  4  cm. 
Put  25  ccm.  of  cone.  HC1  into  the  flask  and  fill  with  dis- 
tilled water.  Cover  the  mouth  of  the  flask  with  a  card 
or  small  square  of  glass  and  invert  in  the  pan  of  water 
outside  the  dish.  Quickly  bring  the  inverted  flask  over 
the  magnesium  in  the  dish  so  as  to  catch  all  the  hydrogen 
liberated  but  allowing  no  air  to  enter  the  flask. 

When   the   metal   is   completely   dissolved,    cover   the 

mouth  of   the  flask  with  the  glass  plate  and  remove  to 

sink  or  deep  vessel  previously  filled  with  water  and  adjust 

the  flask  so  as  to  make  the  level  of  water  the  same  inside 

*  See  Suggestions  to  Teachers. 


80          LABORATORY  MANUAL  IN   CHEMISTRY 

and  outside  the  flask.  Cover  the  mouth  of  the  flask  with 
the  glass  plate,  remove  from  the  bowl  and  place  upright 
on  the  table.  By  pouring  from  a  graduate,  ascertain  the 
volume  of  water  necessary  to  fill  the  flask  even  full.  The 
volume  of  water  added  equals  the  volume  of  hydrogen 
liberated. 

Note  the  temperature  of  the  water  (equal  to  the  tem- 
perature of  the  gas)  and  read  the  barometer.  Subtract 
the  pressure  due  to  water  vapor  (see  text,  p.  410)  from 
the  barometric  reading  to  get  the  real  pressure  of  the 
hydrogen.  Reduce  the  volume  of  hydrogen  to  standard 
conditions  and  calculate  the  weight  of  magnesium  neces- 
sary to  liberate  1  g.  of  hydrogen.  This  result  is  the 
equivalent  of  magnesium  as  obtained  in  your  experiment. 
Repeat  with  another  piece  of  magnesium,  if  time  permits, 
and  average  the  results.  Record  your  results  as  follows : 

EXP.  1  EXP.  2 

Weight  of  magnesium  taken   .     .                g.  g. 

Volume  of  hydrogen  obtained      .                ccra.  ccm. 

Temperature °  ° 

Barometer      ........                mm.  mm. 

Water  vapor  pressure      ....                mm.  mm. 

Pressure  of  hydrogen       ....                 mm.  mm. 

Volume  hydrogen  (standard  con- 
ditions)    ccm.  ccm. 

Equivalent  of  magnesium  .  .  . 
Average 


EXP.  42.    THE  EQUIVALENT  OF  SODIUM 

Apparatus.  Wide  mouth  bottle  of  250-500  ccm.  capa- 
city, pan  of  water,  capsule  (for  holding  sodium)  and  wire 
for  holder  as  shown  in  Fig.  29.  Wire  nail  to  fit  the  cap- 
sule. Stiff  card  or  small  square  of  glass.  Graduate, 
thermometer  and  barometer  for  general  class  use. 


EXPERIMENTS  81 

Procedure.  See  that  the  capsule  is  thoroughly  clean  and 
dry  and  weigh  it  accurately.  Cut  off  any  crust  from 
some  pieces  of  sodium  and  remove  any  oil  with  filter 
paper.  Fill  the  capsule  even  full  with  clean  sodium, 
using  the  head  of  the  nail  to  press  it  tightly  into  the 
capsule,  and  weigh.  Twist  the  wire  firmly  about  the 
capsule,  being  sure  that  it  cannot  drop  out.  Fill  the  bot- 
tle with  water  and  invert  in  the  pan  of  water,  taking  care 
that  no  air  enters.  Lean  the  bottle  against  the  side  of 
the  pan  as  shown  in  Fig.  29,  and  quickly  thrust  the  cap- 
sule, mouth  downward,  under  the 
mouth  of  the  bottle  so  as  to  catch  all 
the  gas  liberated.  When  the  flow 
of  gas  slackens,  tilt  the  capsule  slowly 
so  that  water  may  again  come  in  con- 
tact with  the  sodium,  and  finally  turn 
the  capsule  mouth  upward.  If  care- 
less handling  causes  the  sodium  to  escape  from  the  cap- 
sule, stand  back  until  all  action  ceases. 

When  the  action  is  complete,  measure  the  hydrogen 
evolved  and  take  the  temperature  and  pressure.  Calcu- 
late and  record  the  results  as  directed  in  Exp.  41. 
Repeat  if  time  permits  and  average  the  results. 

EXP.  43.     PREPARATION  OF  AN  ACID   SALT 

Materials.  Cone.  H2SO4.  Solid  KOH.  Phenolphtha- 
lein  solution.  Litmus  paper.  Zinc. 

Apparatus.  Beakers.  Evaporating  dish.  Stirring  rod. 
Graduate  or  20  ccm.  pipette. 

Procedure.  Dissolve  7  g.  of  solid  KOH  in  20  ccm.  of 
water.  Add  10  ccm.  of  cone.  H2SO4  to  40  ccm.  of  water. 
Measure  20  ccm.  of  the  H2SO4  solution  into  an  evaporating 
dish,  add  15  ccm.  of  the  KOH  solution,  and  cool.  To  the 


82          LABORATORY  MANUAL  IN  CHEMISTRY 

mixture  add  a  drop  of  phenolphthalein  solution  and,  stir- 
ring constantly,  neutralize  with  the  remaining  KOH  solu- 
tion added  drop  by  drop,  until  a  faint  pink  color  is 
produced.  Write  an  equation  indicating  what  has  been 
formed.  What  kind  of  a  salt  is  it  ?  What  other  methods 
of  forming  salts  do  you  know? 

To  the  neutralized  solution  now  add  20  com.  of  the 
H2SO4  solution  and  evaporate  until  a  little  of  the  sub- 
stance removed  on  a  glass  rod  solidifies  on  cooling;  then 
remove  from  the  flame  and  cool. 

Note  the  properties  of  the  hydrogen  potassium  sulfate 
thus  formed.  Dissolve  a  bit  of  it  in  water  and  cautiously 
taste  the  solution  and  note  its  action  on  blue  litmus  paper. 
Put  some  of  the  salt  in  a  test  tube  with  a  piece  of  zinc,  add 
a  little  water  and  notice  the  result.  Is  hydrogen  potas- 
sium sulphate  an  acid  as  well  as  a  salt?  Write  an 
equation  indicating  its  formation. 

EXP.   44.    CARBON 

Materials.  Coal,  wood,  paper,  bread,  potato,  vegetables, 
starch,  cotton,  wool,  meat,  candle.  Sand.  Kerosene. 
Powdered  wood  charcoal.  Animal  charcoal.  Hydrogen 
sulfid  water.  Dark  brown  sugar.  Copper  oxid,  CuO. 
Lime  water,  Ca(OH)2. 

Apparatus.  Clay  crucible  or  iron  dish.  Ring  stand 
or  tripod.  Beakers.  Test  tube  with  cork.  Funnel.  A 
hard  glass  test  tube  fitted  with  stopper  and  exit  tube  as 
explained  in  (<?).  Pincers. 

Procedure,     (a)    The  occurrence  of  carbon. 

1.  (Hood.)  Place  a  thin  layer  of  sand  in  a  clay  cruci- 
ble or  small  iron  pan  and  on  it  put  small  pieces  of  some  of 
the  animal  and  vegetable  material  first  listed  above,  dif- 
ferent students  using  different  materials.  Cover  this 


EXPERIMENTS  83 

material  with  sand  to  protect  it  from  the  action  of  the  air 
(Why  ?),  or  else  place  a  cover  on  the  crucible  or  pan. 
Support  on  a  ring  stand  and  heat  strongly  until  all  smok- 
ing ceases;  then  cool  and  examine. 

One  of  two  things  will  happen.  The  material  will 
sometimes  be  volatilized;  more  often  it  will  be  dscom- 
posed,  leaving  a  residue  of  charcoal.  What  happens  with 
the  substances  you  tried  ?  Hold  some  of  the  black  residue 
in  the  top  of  a  Bunsen  flame.  Does  it  burn  up  as  char- 
coal does  ? 

2.  Hold  a  cold  glass  tube  in  the  yellow  Bunsen  flame 
and  the  flame  of  a  candle  and  of  kerosene.  What  is  de- 
posited on  the  cold  glass  ?  Where  did  it  come  from,  the 
air  or  the  burning  substance  ?  Name  one  element  that 
the  common  liquid  or  gaseous  fuels  contain  as  shown  by 
your  experiments.  Point  out  one  similarity  in  composi- 
tion between  the  fuels  we  burn  and  the  foods  we  eat. 

(6)   The  properties  of  amorphous  carbon. 

1.  Fill  a  test  tube  one  quarter  full  of  powdered  wood 
charcoal   and   pour  into   it    5   ccm.  of  water  containing 
hydrogen  sulfid.     Cork  the  tube   and  shake  thoroughly 
from  time  to  time  for  15  minutes.     Then  note  whether 
the  odor  is  gone.     If  not,  add  more  charcoal  and  repeat 
the  shaking  until  the  odor  disappears.     State  one  reason 
why  charcoal  is  used  in  water  filters. 

2.  Dissolve  25  g.  of  brown  sugar  in  100  ccm.  of  water 
and  note  color  of  solution.     Add  10  g.  of  animal  charcoal 
and  boil  for  15  minutes;  then  filter.     Note  color  of  fil- 
trate and  taste  it.     Is  the  sugar  still  there  ?     Repeat  the 
treatment,  if  necessary,  until  the  solution  is  nearly  color- 
less.     Why  is  animal  charcoal  used  in  refining  sugar  and 
other  substances  ? 

(Use  the  sugar  solution  for  Exp.  No.  51,  and  start  the 


84    LABORATORY  MANUAL  IN  CHEMISTRY 

fermentation  to-day,  allowing  it  to  continue  until  you  are 
ready  to  distill  the  mixture.) 

(c)   Carbon  as  a  reducing  agent. 

Mix  5  g.  of  copper  oxid  intimately  with  an  equal  bulk 
of  powdered  charcoal,  and  heat  the  mixture  strongly  in  a 
hard  glass  test  tube,  fitted  with  an  exit  tube  so  arranged 
that  the  gas  liberated  may  bubble  into  5  ccm.  of  lime 
water  in  a  test  tube.  The  precipitate  obtained  in  the 
lime  water  indicates  carbon  dioxid  (see  Exp.  46  d). 
Sometimes  a  red  glow  appears  inside  the  test  tube  as 
though  its  contents  were  on  fire.  After  heating  5-10 
minutes,  cool,  and  pour  out  the  contents  upon  the  desk. 
What  is  the  reddish  material?  What  becomes  of  the 
charcoal?  Write  an  equation  expressing  the  reaction 
between  charcoal  arid  copper  oxid. 

EXP.   45.    MANUFACTURE  OF  ILLUMINATING  GAS 

Instructor's   Experiment 

Material.     Soft  coal.     Lead  acetate.     Litmus  paper. 

Apparatus  as  shown  in  Fig.  25,  except  that  the  test  tube 
must  be  of  hard  glass  and  the  exit  tube  bent  at  a  right 
angle,  allowing  the  test  tube  to  lie  horizontally. 

Procedure.  Fill  the  hard  glass  test  tube  half  full  of 
chunks  (not  dust)  of  soft  coal  and  set  up  the  apparatus. 
Place  pieces  of  moist  red  litmus  paper  and  of  filter  paper 
moistened  with  lead  acetate  solution  on  opposite  sides  of 
the  side-neck  test  tube,  the  ends  projecting  from  the 
mouth  of  the  tube  so  that  they  will  be  held  in  position  by 
the  stopper  when  inserted.  Heat  the  coal  gently  at  first, 
then  strongly,  and  collect  the  gas  evolved  over  water, 
noting  its  properties.  Does  it  seem  similar  to  the  gas 
coming  from  the  gas  pipes? 


EXPERIMENTS  85 

Different  processes  for  making  gas  for  fuel  or  illumina 
tion  are  used  in  different  localities.  How  is  it  made  in 
your  city  and  from  what  material?  Why  is  this  process 
or  material  used  rather  than  another? 

What  collects  in  the  side-neck  test  tube?  Note  and 
explain  any  change  in  the  papers.  What  makes  the  red 
litmus  turn  blue?  Hydrogen  sulfid  is  usually  present, 
causing  the  formation  of  black  lead  sulfid  when  it  conies 
in  contact  with  lead  acetate.  Complete  the  equation  and 
name  the  other  product  of  the  reaction. 

Pb(C2H302)2  +  H2S->PbS  +  

EXP.  46.     CARBON  DIOXID,  C02,  AND  CARBONIC  ACID, 

H2C03 

Materials.  Marble  or  limestone,  CaCO3.  Cone.  HC1. 
Lime  water,  Ca(OH)2.  Wooden  splint.  Bread.  Candle. 

Apparatus  such  as  was  used  in  making  hydrogen, 
Fig.  13.  Test  tubes.  Beaker.  Wire.  Litmus  paper. 

Procedure,     (a)  Preparation. 

Put  10-20  g.  of  marble  or  limestone  into  the  generat- 
ing bottle,  add  50  ccm.  of  water,  insert  the  stopper  and 
through  the  thistle  tube  pour  5  ccm.  of  cone.  HC1.  Col- 
lect three  bottles  of  gas,  adding  more  acid  from  time  to 
time  if  necessary  to  hasten  the  action.  Complete  the 
equation : 

CaCO3  +  —  HC1  -> +  H2CO3  -> +  CO2 

Any  of  the  common  acids  may  take  the  place  of  HC1  in 
this  reaction.     Why  ? 

(5)  Physical  properties. 

Note  the  color,  odor,  and  taste  of  carbon  dioxid  and 
ascertain  whether  it  will  burn  or  support  combustion. 


86          LABORATORY  MANUAL  IN  CHEMISTRY 

Set  a  lighted  candle  in  a  bottle  of  air  and  invert  over  it 
a  bottle  of  carbon  dioxid.     Explain  the  result. 

(<?)    Chemical  properties. 

1.  Put  a  piece  of  blue  litmus  paper  into  a  little  watei 
and  let  carbon  dioxid  bubble  into  it.     Explain  what  hap- 
pens.    Is  carbon  dioxid  an  acid  anhydrid  ? 

2.  Add  an  equal  volume  of  lime  water  to  the  solution 
just  formed  and  explain  what  happens. 

3.  Shake  the  mixture  obtained  in  (2)  and  pour  out  all 
but  5  ccm.  and  continue  to  pass  the  carbon  dioxid  through 
this  volume.     What  happens  ?     Acid  calcium  carbonate, 
soluble  in  water,  is  formed. 

Complete  the  following  equations  expressing  the  changes 
which  have  taken  place  and  write  similar  equations  show- 
ing the  products  formed  when  CO2  is  absorbed  by  NaOH. 

C02+H20-> 

Ca(OH)2  +  H2CO3  -> + 

CaC03  +  H2C03  ->  CaH2(CO3)2 

(c?)   Testing  for  carbon  dioxid. 

When  treated  with  HC1,  any  carbonate  liberates  carbon 
dioxid  just  as  marble  does.  The  formation  of  a  precipitate 
in  lime  water  is  a  test  for  carbon  dioxid  and  carbonates. 
Carbon  dioxid  is  so  heavy  that  it  may  be  poured  from  one 
bottle  to  another  just  like  water,  as  the  following  experi- 
ment shows. 

1.  Pour  about  20  ccm.  of  lime  water  into  a  bottle  and 
shake  it.     No  significant  change  should  occur,  though,  on 
long   standing,  lime  water  shows  the  presence  of  small 
amounts  of  carbon  dioxid  in  the  air.     (Try  it.)     Pour  a 
bottle  of   carbon  dioxid   into  the  lime  water   and  shake 
again.     What  happens  ? 

2.  Hold  a  burning  wooden   splint    in   a  bottle   of  air 


EXPERIMENTS  87 

until  it  is  extinguished,  add  a  little  lime  water  and  shake. 
What  is  the  result  ?  Where  did  the  carbon  dioxid  come 
from  ? 

3.  Stick  a  piece  of  bread  on  a  wire,  hold  it  in  a  flame 
until  it  takes  fire,  then  lower  it  into  another  bottle  of  air. 
When  the  flame  goes  out,  test  with  lime  water  as  before 
and  explain  where  the  carbon  dioxid  comes  from. 

4.  Blow  the  breath  through  a  glass  tube  into  a  little 
lime  water.      Explain  the  result.      How  was  the  carbon 
dioxid  in  the  breath  produced  ?     What  similarity  is  there 
in  the  burning  of  coal  or  wood  under  the  boilers  of  an 
engine  and  the  use  of  food  in  the  body  ?     Why  is  the  tem- 
perature  produced   higher  in   one  case  than  the  other  ? 
What  causes  the  body  temperature  to  be  higher  than  that 
of  the  atmosphere  ? 

EXP.  47.    CARBON  MONOXID 

Instructor's  Experiment 

Materials.     Charcoal.     Oxygen.    NaOH.     Lime  water. 

Apparatus  as  shown  in  Fig.  12,  except  that  the  iron 
pipe  is  replaced  by  a  combustion  tube  of  hard  glass. 
This  is  supported  in  the  furnace  on  a  strip  of  sheet  iron 
to  prevent  sagging  of  the  tube  when  heated.  In  place  of 
the  boiling  flask  a  2-liter  bottle  is  attached  to  the  com- 
bustion tube  by  means  of  an  exit  tube,  passing  through 
a  2-hole  rubber  stopper  fitting  the  neck  of  the  bottle. 
Through  the  other  hole  in  the  stopper  passes  an  inlet  tube 
reaching  to  the  bottom  of  the  bottle,  the  outer  end  being 
connected  to  the  water  tap.  Short  piece  of  rubber  tubing. 
Pinch  cock. 

Procedure.  Fill  the  2-liter  bottle  with  oxygen  by  dis- 
placement of  water  and  insert  the  stopper  carrying  the 
inlet  and  exit  tubes.  Close  the  inlet  tube  with  a  piece  of 


88          LABORATORY  MANUAL  IN  CHEMISTRY 

rubber  tubing  and  a  pinch  cock.  Fill  the  combustion 
tube  with  small  pieces  of  wood  charcoal  *  (no  dust)  and 
connect  it  to  the  oxygen  bottle.  Pour  NaOH  solution 
into  the  wash  bottle  until  the  end  of  the  inlet  tube  is  cov- 
ered to  the  extent  of  1  cm. 

Heat  up  the  combustion  tube  moderately  to  begin  with, 
lighting  the  center  burners  first.  All  joints  must  be 
tight,  as  will  be  indicated  by  bubbles  passing  through 
the  NaOH  solution.  When  the  tube  is  hot,  connect  the 
inlet  tube  of  the  oxygen  bottle  to  the  water  tap,  so  that 
as  water  enters,  oxygen  will  be  forced  slowly  over  the 
heated  charcoal.  Regulate  the  size  of  the  stream  so  that, 
it  takes  from  10—15  minutes  to  fill  the  bottle  with  water. 
Collect  two  or  three  bottles  of  carbon  monoxid  over  water 
as  it  escapes  from  the  apparatus.  When  the  oxygen  bottle 
is  full  of  water,  shut  off  the  water,  disconnect  the  combus- 
tion tube  at  both  ends,  and  turn  off  the  gas  in  the  furnace. 

(CAUTION  :  Carbon  monoxid  is  poisonous.  Avoid 
breathing  the  gas  !) 

Note  the  color  and  odor  of  the  gas  and  ascertain 
whether  it  will  burn  and  support  combustion.  Describe 
the  flame  produced. 

Introduce  25  com.  of  lime  water  into  a  bottle  full  of 
carbon  monoxid  and  shake.  Is  there  any  reaction  ? 
How  could  you  tell  the  difference  between  carbon 
monoxid  and  carbon  dioxid?  Set  fire  to  this  same  bottle 
of  gas  and  shake  the  lime  water  with  the  products  of 
combustion  after  the  flame  has  gone  out.  What  hap- 
pens ?  To  what  does  carbon  monoxid  burn  ? 

*  Ordinarily  charcoal  has  not  been  distilled  at  a  sufficiently  high  tem- 
perature to  remove  all  volatile  material.  Before  performing  this  experi- 
ment it  is  well  to  heat  the  charcoal  in  the  combustion  tube  in  the 
furnace  while  passing  a  slow  current  of  hydrogen  through  the  tube.  In 
this  way  considerable  tarry  matter  will  be  removed. 


EXPERIMENTS  89 

Discussion.  When  oxygen  and  carbon  come  together 
inside  the  combustion  tube,  the  latter  burns  just  as  it 
does  in  air,  forming  carbon  dioxid.  As  this  gas  passes 
over  the  hot  carbon  it  is  reduced  to  carbon  monoxid. 
The  sodium  hydroxid  wash  bottle  is  to  remove  any  un- 
changed carbon  dioxid.  Write  equations  indicating  all 
reactions  taking  place. 

Explain  in  detail  how  in  a  similar  way  carbon  monoxid 
is  produced  by  coal  stoves  or  charcoal  braziers,  sometimes 
causing  death  to  the  inmates  of  the  house.  If  carbon 
monoxid  is  burned,  is  this  danger  removed  ? 

EXP.  48.    BURNING  AND  SUPPORTING  COMBUSTION 

Instructor's  Experiment 

Materials.     Wooden  splints. 

Apparatus.  A  piece  of  moistened  cardboard  having  a 
hole  in  the  center,  placed  on  top  of  a  lamp  chimney  fitted 
with  a  stopper  pierced  by  two  tubes  as  shown 
in  Fig.  30.  The  tube  A  is  wider  and  shorter 
than  6r.  Clamp  and  ring  stand. 

Procedure.  Support  the  chimney  in  a  ver- 
tical position  by  means  of  a  clamp  and  ring 
stand.  Connect  the-  tube  6r  to  a  gas  jet  and 
allow  illuminating  gas  to  flow  at  full  pressure 
into  the  apparatus  for  a  moment.  Then  turn 
the  gas  partly  off  and  light  it  as  it  escapes  "  ^  " A 
from  the  hole  in  the  cardboard.  Thrust  a 
lighted  wooden  splint  up  into  the  tube  A.  Describe  and 
explain  what  happens.  What  difference  is  there  in  the 
chemical  reaction  taking  place  within  and  without  the 
chimney  ?  What  other  gases  which  you  know  might  be 
substituted  (a)  for  the  illuminating  gas  ;  (£)  for  the  air  ? 
Under  what  conditions  is  it  said  that  a  substance  burns 


90    LABORATORY  MANUAL  IN  CHEMISTRY 

and  another  supports  combustion  ?      Under  what  condi- 
tions could  you  reverse  the  statement  ? 

EXP.   49.    FLAMES 

Materials.  Powdered  charcoal.  Piece  of  cardboard 
10-15  cm.  square.  HNO3. 

Apparatus.  Bunsen  burner.  Copper  wire.  Blowpipe, 
or  glass  tube  50  cm.  long  from  which  to  make  it.  Short 
piece  of  glass  tube. 

(&)    Why  a  flame  gives  light. 

1.  Notice  the  blue  flame  of  a  Bunsen  burner.     Does  it 
give  considerable  light  ? 

2.  Hold  a  piece  of  wire  or  glass  tube  in  the  flame,  and 
notice  how  it  emits  light  as  it  becomes  hot.     What  would 
be  the  effect  on  the  luminosity  of  the  flame  if  it  should 
become  filled  with  hot  solid  particles  ?     By  knocking  to- 
gether  two  blackboard  erasers,  fill  the  flame  with  fine 
dust  and  note  the  effect.     Throw  some  powdered  char- 
coal into  the  flame  and  note  the  effect. 

3.  Close  the  air  holes  at  the  bottom   of   the    Bunsen 
burner  and  notice  the  change  in  luminosity  of  the  flame. 
Are  there  any  visible  solid  particles  which  can  cause  it 
to  emit   light?     Hold  in  the   flame   a   cold   glass   tube. 
What   solid  material  is  deposited?     Could  it  have  been 
the  source  of  the  light  of  the  flame  ?     What  becomes  of 
it  when  the  flame  is  not  interfered  with?     From  what  is 
it   formed    in   the   flame?      Why   is    an   ordinary   flame 
luminous  ? 

(5)   The  structure  of  a  flame. 

1.  Note  the  structure  of  a  Bunsen  flame  as  shown  in 
Fig.  31. 


EXPERIMENTS  91 

2.  Using  a  Bunsen  flame  with  a  sharp  inner  cone,  Gr, 
about  an  inch  high,  hold   a   piece   of   cardboard   in   the 
center  of  -the  flame,  first  vertically,   resting  the 
cardboard  on  the  top  of  the  burner  tube ;  secondly, 
horizontally,  about  an  inch  above  the  top  of  the 

tube.  As  soon  as  the  cardboard  begins  to  char, 
remove  it  quickly  from  the  flame  before  it  takes 
fire.  The  charred  outlines  are  cross-sections  of 
the  flame,  indicating  the  hotter  parts. 

3.  Prove  that  the  inner  cone,    6r,   consists   of 
unburned  gas  by  holding  a  glass  tube  in  it  as 
shown  in  Fig.  32,  and  light  the  gas  as  it  issues  FlG 
from  the  tube. 

4.  Clean  a  piece  of  copper  wire  by  dipping  it  in  HNO3 
for  a  moment,  then  washing  in  water.     Hold  one  end  of 

this  wire  in  the  top  of  the  flame  and  explain 
why  it  turns  black.  Lower  the  wire  to  a 
point  just  above  the  inner  cone  and  observe 
and  explain  how  the  original  coppej1  color 
returns.  Remove  the  wire  from  the  flame 
and  note  how  the  hot  copper  turns  black  in 
the  air  before  it  cools.  Explain. 

(c)   The  blowpipe  flame. 

If  one  is  not  already  available,  make  a 
piece  of  glass  tubing  of  the  size  and  shape 
shown  in  D,  Fig.  5,  and  draw  out  the 
shorter  end  as  shown  in  Fig.  3.  Cut  the 
slender  part  straight  across  so  as  to  form  a  tip  with  an 
opening  not  larger  than  the  diameter  of  a  pin.  Thus 
you  have  made  a  blowpipe.  Preserve  it  for  use  in  later 
experiments. 

Turn  down  the  gas  in  a  Bunsen  burner  until  a  yellow 
flame  about  4  cm.  high  results.     Hold  the  blowpipe   as 


92 


LABORATORY  MANUAL  IN  CHEMISTRY 


FIG.  33. 


shown  in  Fig.  33,  and 
blow  gently.  When  the 
breath  is  nearly  ex- 
hausted, use  the  cheeks 
as  a  bellows  while  in- 
haling a  fresh  breath 
through  the  nose.  With 
a  little  practice  a  steady, 
narrow,  very  hot  flame 
may  be  obtained.  Note 
that  the  blowpipe  flame 
has  the  same  structure 
as  the  blue  Bunsen 
flame.  The  oxidizing  flame  may  be  increased  in  size  and 
the  reducing  flame  diminished  by  blowing  somewhat 
stronger,  and  vice  versa. 

EXP.  50.    HYDROCARBONS 

Materials.  Kerosene.  Candle.  Cobalt  chlorid  solution. 
Calcium  carbid,  CaC2.  Lime  water,  Ca(OH)2.  Red  lit- 
mus paper.  Gasoline  or  benzine.  Lard,  tallow,  or  but- 
ter. Filter  paper. 

Apparatus.  Small  flask  with  stopper.  Two  wide-mouth 
bottles.  Glass  plate.  Two  watch  glasses  or  evaporating 
dishes. 

(#)    Composition. 

Procedure.  1.  Fill  a  small  flask  full  of  cold  (ice)  water 
and  cork  it  tightly.  Wipe  the  flask  dry  and  hold  it  over 
the  flame  of  burning  gas,  kerosene,  and  a  candle.  Wipe 
off  the  moisture  in  each  case  with  a  piece  of  cobalt  chlorid 
test  paper.  What  is  indicated  in  each  case  ?  How  was 
it  formed  ?  Where  must  the  hydrogen  have  come  from, 
the  air  or  the  burning  material?  Outline  a  general 


EXPERIMENTS  93 

method  for  ascertaining  whether  a  burning  substance 
contains  hydrogen. 

2.  Hold  a  piece  of  cold  glass  tubing  in  the  yellow  flame 
of  gas,  kerosene,  and  a  candle.  What  is  deposited  in 
each  case  ? 

The  common  gaseous  and  liquid  fuels  consist  almost 
wholly  of  the  two  elements  indicated.  What  are  the 
final  products  of  combustion  when  carbon  and  hydrogen 
burn  ?  Write  equations  indicating  the  products  formed 
when  illuminating  gas  (consisting  mainly  of  CH4  and  H2) 
burns.  Write  a  similar  equation  for  the  burning  of  kero- 
sene, assuming  it  to  have  the  formula  C10H22. 

(5)    Common  gaseous  hydrocarbons. 

1.  Fill  a  wide-mouth  bottle  one  seventh  full  of  illumi- 
nating gas  by  displacement  over  water.     Raise  the  bottle 
from  the  water  for  a  moment  and  allow  air  to  displace  the 
remaining  water.     Cover  with  a  glass  plate  and  stand 
upright  on   the  table.     Remove  the  plate   and   bring  a 
flame  to  the  mouth  of  the  bottle.     What  happens  ?     Why 
does  the  gas  explode  now  though  it  burns  quietly  in  the 
burners  ? 

2.  Fill  a  test  tube  and  invert  in  a  dish  of  water.    Drop 
a  small  piece  of  calcium  carbid  into  the  dish  and  quickly 
collect  the  liberated  acetylene.     Note  its  odor.     Close  the 
test  tube  with  the  thumb  and  bring  to  a  flame.     Describe 
how  acetylene  burns.     What  is  deposited  by  the  flame  ? 
Calculate  the  percentage  composition  of  acetylene  and  of 
methane,  CH4,  the  chief  constituent  of  illuminating  gas, 
and  see  if  you  can  get  an  idea  why  one  deposits  more  soot 
than  another.     Test  the  water  left  in  the  dish  with  red 
litmus  paper.    Complete  the  equation  and  figure  out  what 
is  present. 

CaC2  +  2  H2O->C2H2  + 


94          LABORATORY  MANUAL  IN  CHEMISTRY 

(c)    Common  liquid  hydrocarbons. 

CAUTION:  Keep  the  bottles  containing  gasoline  and 
benzine  away  from  all  flames  ! 

1.  Pour  1  ccm.  (25  drops)  of  kerosene  into  a  watch 
glass  or  evaporating  dish  and  the  same  volume  of  gasoline 
or  benzine  into  another  and  note  the  time  it  takes  each  to 
evaporate.     Which  is  the  more  volatile? 

2.  Pour  not  more  than  25  drops  of  gasoline  or  benzine 
into  a  wide-mouth  bottle,  shake  well,  stand  upright  on 
the  table  and  bring  a  flame  to  the  mouth  of  the  bottle. 
Explain   what   happens.       Treat    similarly    25   drops   of 
kerosene  and  explain  the  difference  in  the  results.     Why 
is  it  that  explosions  happen  so  frequently  with  benzine 
and  gasoline  ? 

3.  Try  the  solubility  of  fats,  such  as  lard,  tallow,  or 
butter,  in  benzine  or  gasoline.     Why  are  these  liquids 
used  in  "  dry  cleaning  "  ? 

EXP.  51.     ALCOHOL   AND    ACETIC  ACID   BY   FERMENTA- 
TION 

Materials.  Brown  sugar,  or  sugar  solution  from  Exp. 
44.  Yeast  cake.  Sodium  acetate,  NaC2H3O2.  Cone. 
H2SO4.  Alcohol,  C2H5OH.  Lime  water,  Ca(OH)2. 

Apparatus  consisting  of  a  liter  flask  fitted  with  an 
exit  tube  leading  into  a  small  flask  used  as  a  wash  bottle. 
This  wash  bottle  containing  lime  water  is  protected  from 
the  air  by  having  its  exit  tube  dip  into  water  in  a  test  tube. 
Distillation  apparatus  as  shown  in  Fig.  18.  Evaporating 
dish. 

Procedure,     (a)  Alcohol 

With  a  little  water  rub  into  a  thin  paste  a  quarter  of  a 
cake  of  yeast  and  add  it  to  the  sugar  solution  used  in 


EXPERIMENTS  95 

Exp.  44,  adding  more  sugar  until  you  have  about  50  g.  in 
500  com.  of  water.  Set  up  the  apparatus  as  directed 
above,  placing  the  sugar  solution  in  the  large  flask  and 
about  50  ccm.  of  lime  water  in  the  small  flask.  Add  just 
enough  water  to  the  test  tube  to  cover  the  end  of  the  exit 
tube.  Allow  to  stand  in  a  warm  place  (25-30°  C.)  for 
about  a  week. 

Fermentation  is  soon  indicated  by  bubbles  of  gas  ap- 
pearing in  the  sugar  solution  and  later  passing  into  the 
lime  water r  What  is  the  gas  liberated,  judging  by  the 
reaction  in  the  lime  water?  (If  no  reaction  is  noted, 
the  apparatus  leaks.) 

Leaving  the  sediment  in  the  bottom  of  the  fermentation 
flask,  decant  two  thirds  of  the  liquid,  and  distill  it  at  as 
low  a  temperature  as  possible  until  about  20  corn,  of  dis- 
tillate are  obtained.  This  should  consist  of  alcohol  mixed 
with  some  water.  A  second  distillation  and  collection  of 
the  first  half  of  the  distillate  will  reduce  the  proportion  of 
water,  which  may  be  removed  completely  by  allowing  the 
mixture  to  stand  for  some  time  over  quicklime.  This 
treatment  will  ordinarily  not  be  necessary  to  get  evidence 
of  the  presence  of  alcohol  by  the  following  tests. 

Pour  the  distillate  into  an  evaporating  dish  and  dip  a 
piece  of  filter  paper  in  it.  Set  fire  to  the  paper,  drop  it 
into  the  dish,  and  note  the  character  of  the  alcohol  flame. 
If  the  filter  paper  will  not  take  fire,  too  much  water  is 
present.  Pour  the  distillate  into  a  test  tube,  warm  nearly 
to  boiling,  and  bring  the  mouth  of  the  tube  to  a  flame. 
The  alcohol  will  be  volatilized  (b.  p.  78°)  and  burn  at  the 
mouth  of  the  tube. 

(5)  Acetic  acid. 

1.  Allow  the  remainder  of  the  mixture  in  the  fermen- 
tation flask  to  stand  open  to  the  air  for  several  weeks, 


96    LABORATORY  MANUAL  IN  CHEMISTRY 

rioting  the  odor,  and  testing  with  blue  litmus  from  time 
to  time.  The  characteristic  sour  smell  of  acetic  acid,  the 
active  constituent  in  vinegar,  will  develop  eventually. 

2.  Add  5  ccm.  of  cone.  H2SO4  to  1  g.  of  any  acetate, 
and  warm.  Note  the  sour  odor  of  the  acetic  acid  that 
is  liberated.  Add  3  ccm.  of  alcohol  and  warm  again. 
Note  the  sweet  odor  of  ethyl  acetate.  Both  of  these 
reactions  are  used  as  tests  for  acetates.  Complete  the 
equations  : 

2  NaOOC.CH3  +  H2SO4-»  -  +  - 


EXP.  52.    SOAP 

Materials.  Lard,  tallow,  or  cottonseed  or  olive  oil. 
Solid  NaOH;  also  solution.  Alcohol.  HC1. 

Apparatus.     A  porcelain  dish  and  ring  stand. 

Procedure.  In  the  porcelain  dish  dissolve  2  g.  of  NaOH 
in  20  ccm.  of  water,  add  about  10  g.  of  the  fat  and  20  ccm. 
of  alcohol,  and  boil  gently  until  the  odor  of  alcohol  is 
gone  and  the  contents  of  the  dish  is  a  pasty  mass. 

The  alcohol  takes  no  part  in  the  chemical  action,  but 
serves  to  dissolve  both  the  fat  and  the  sodium  hydroxid, 
so  that  they  act  more  rapidly  on  each  other.  In  practical 
soap-making  no  alcohol  is  used.  Complete  the  equation, 
and  write  the  name  of  each  substance  beneath  its  formula  : 


—  NaOOC.C17H35 

What  is  soap,  stated  in  chemical  terms  ?  Do  you  see 
any  similarity  between  the  reaction  by  which  soap  is  made 
and  the  reaction  of  alkalies  on  ammonium  salts  (p.  78)  ? 

Dissolve  some  of  the  resulting  substance  in  warm  water 
and  test  it  with  the  fingers.  Does  it  appear  to  be  soap  ? 


EXPERIMENTS  97 

To  some  of  the  soap  solution  add  HC1,  and  shake  vig- 
orously. The  curdy  substance  that  forms  is  a  mixture  of 
stearic  with  other  organic  acids.  Remove  the  curdy  ma- 
terial to  a  test  tube,  add  NaOH  solution,  and  warm. 
Explain  why  the  precipitate  dissolves,  and  what  is 
formed. 

EXP.  53.     CONSTITUENTS  OF  FOODS 

Materials.  Cottonseed  or  olive  oil,  or  lard  or  butter. 
Corn  meal.  Raw  egg.  Hard  boiled  egg.  Meat.  Milk. 
Nuts.  Cheese.  Peas  or  beans.  Starch.  Flour.  Bread. 
Cane  sugar.  Glucose  or  some  sirup.  Fruit.  Potato. 
Vegetables.  Filter  paper,  cotton,  linen,  hemp,  silk,  wool. 
Mixed  cotton  and  woolen  goods.  Ether  or  benzine. 
H2S04.  HN03.  NaOH.  NH4OH.  Water  solution  of 
iodin.  Fehling's  solution  made  from  tablets  or  prepared 
by  dissolving  9  g.  of  copper  sulfate  crystals,  45  g.  of 
Rochelle  salt,  and  20  g.  of  sodium  hydroxid  in  1000  ccm. 
of  water. 

Apparatus.  Unglazed  paper.  Litmus  paper.  Test 
tubes.  Beaker.  Funnel.  Watch  glass  or  evaporating 
dish.  Porcelain  crucible.  Pipestem  triangle. 

Procedure .     (a)    Fats. 

1.  (CAUTION:     Keep    ether    or    benzine    away    from 
flames!)     To  an  eighth  of  a  test  tube  full  of  corn  meal, 
add  10  ccm.  of  ether  or  benzine,  cork,  and  allow  to  stand  10- 
15  minutes.     Then  filter  into  a  watch  glass  or  evaporating 
dish  and  stand  in  a  draught  of  air  to  evaporate.     Note 
what  is  left.     Does  it  seem  to  be  a  fat  or   oil?     This 
method  is  used  as  a  test  for  fat. 

2.  A  simpler  method  of  detecting  considerable  fat  is  as 
follows:     Put  a  drop  of  fat  on  a  sheet  of  unglazed  paper, 
hold  to  the  light,  and  note  the  effect.     Press  a  piece  of  the 


98    LABORATORY  MANUAL  IN  CHEMISTRY 

yolk  of  hard-boiled  egg  upon  the  paper;  after  a  moment 
scrape  it  off  and  hold  to  the  light  as  before.  Does  yolk 
give  a  test  for  fat?  Warming  will  sometimes  help  this 
test  by  melting  the  fat  contained  in  the  substance. 

3.  Test  2  or  3  other  foods  for  fat,  different  students 
using  different  foods. 

(5)      Carbohydrates. 

1.  Sugar.  Examine  and  taste  glucose,  noting  its  proper- 
ties. It  is  difficult  to  crystallize  and  is  not  usually  seen 
in  solid  form.  Most  sirups  consist  mainly  of  glucose. 

Heat  10  ccm.  of  Fehling's  solution  to  boiling,  add  a 
little  glucose,  boil  again,  and  note  the  result.  This  pro- 
cedure is  used  as  a  test  for  sugar.  (Several  sugars  do  not 
give  this  test,  though  the  common  ones  do,  when  properly 
treated.)  If  much  sugar  is  present,  it  can  be  detected  by 
the  taste. 

Examine  and  taste  cane  sugar,  noting  its  properties.  It 
crystallizes  readily.  Heat  10  ccm.  of  Fehling's  solution 
to  boiling  as  before  and  add  a  few  grains  of  cane  sugar. 
Does  it  give  the  test  ? 

Dissolve  1  g.  of  cane  sugar  in  10  ccm.  of  water,  add  1 
drop  of  H2SO4  and  boil  for  5-10  minutes.  Then  add  10 
ccm.  of  Fehling's  solution  and  boil  again.  Does  it  give 
the  test  for  sugar  now  ? 

Test  2  or  3  foods  for  sugar,  boiling  with  acid  if  it  does 
not  give  the  test  without  this  treatment. 

When  boiled  with  any  acid,  cane  sugar  is  converted  into 
glucose,  and  levulose,  a  body  resembling  glucose  closely. 
Explain  how  a  food  may  taste  sweet,  yet  not  give  Fehling's 
test  for  sugar  until  after  it  is  boiled  with  acid. 

In  making  taffy,  caramels,  butter  scotch,  etc.,  what  is 
the  use  of  the  vinegar  or  other  acid  added  before  boiling  ? 
If  you  wanted  the  candy  to  "sugar"  quickly,  i.e.  eryss- 


EXPERIMENTS  99 

tallize  well,  would  you  boil  the  mixture  with  vinegar  or 
other  acid  ?     Why  ? 

Fehling's  solution  consists  essentially  of  cupric  oxid 
dissolved  in  a  solution  of  an  alkaline  tartrate.  When 
boiled  with  glucose  the  cupric  oxid,  CuO,  is  reduced  to 
cuprous  oxid,  Cu2O,  which  is  not  soluble  in  the  tartrate 
solution  and  is  precipitated  as  a  red  powder. 

2.  Starch.     Notice  the  properties  of  starch.     Moisten 
it  with  a  water  solution  of  iodin  and  describe  the  result. 
Grind  1  g.  of  starch  to  a  fine  powder,  make  into  a  thin 
paste  with  10  ccm.  of  water,  then  pour  the  mixture  into 
100  ccm.  of  boiling  water  and  boil  5  minutes..     Cool  a  por- 
tion of  the  boiled  starch  paste  in  water  and  then  add  a  drop 
of   iodin  solution.     Result?     Does  the  iodin  produce  a 
more  striking  effect  on  boiled  starch  than  when  it  is  not 
boiled  ?     The  blue  color  given  by  iodin  is  a  test  for  starch. 
Heat  destroys  the  color. 

Test  two  or  three  foods  for  starch,  both  before  and  after 
boiling. 

3.  Cellulose.     Examine  filter  paper,  cotton,  linen,  hemp, 
etc.,  and  note  the  properties  of  cellulose,  especially  its 
toughness.     Note  how  readily  it  burns  when  dry,  without 
fumes  or  much  smoke  and  without  swelling  up. 

The  fibrous  matter  in  vegetable  material  is  cellulose. 
Wood  and  grass  contain  much,  sometimes  also  celery  and 
parsnips.  Other  vegetables  contain  little  unless  they  have 
become  "pithy,"  i.e.  full  of  cellulose.  It  is  not  digested 
by  human  beings,  hence  is  of  no  value  as  a  food  con- 
stituent. Many  animals  utilize  it  as  food,  however. 

(c)    Proteid. 

1.  Heat  some  silk,  wool,  meat,  peas  or  beans  and  notice 
how  the  material  swells  up  as  it  burns.  Note  the  smoke 
and  the  odor  produced.  Compare  with  cellulose. 


100        LABORATORY  MANUAL  IN   CHEMISTRY 

2.  Heat  one  of  the  above  in  a  test  tube,  noting  the 
odor  produced.     Hold  a  piece  of  red  litmus  in  the  fumes 
in  the  tube.     What  happens  ?     Explain  why. 

3.  Shake  a  little  albumen  (raw  white  of  egg)  with  water 
in  a  test  tube.     It  goes  into  solution,  does  it  not  ?     (Many 
proteids  are    soluble  in   water.)       Heat  the   mixture  to 
boiling  and  note  result.      Proteids  are  coagulated  by  boil- 
ing.    What  is  the  scum  that  forms  when  milk,  meat,  and 
many  vegetables  and  fruits  are  boiled  ?    This  is  frequently 
rejected.     Do  you  think  it  contains  nutrient  material  ? 

4.  Warm  some  of  the  white  of  a  hard-boiled  egg  with 
HNO3  for  a  moment,  pour  off  the  acid  into  another  test 
tube,  and  note  the  color  produced.     Add  NH4OH  to  the 
egg  and  note  the  effect.     The  yellow  color  produced  by 
nitric  acid  is  a  test  for  proteid. 

5.  Test  2  or  3  other  foods  for  proteid,  different  students 
using  different  materials. 

(d)  Mineral  matter. 

(Hood.)  Heat  some  one  of  the  foods  you  have  been 
testing  in  a  porcelain  crucible  without  cover  over  the 
Bunsen  flame  until  the  black  color  due  to  carbonization 
has  disappeared.  Is  there  much  ash  left  ?  An  incombus- 
tible residue  left  after  burning  is  a  test  for  mineral  matter. 

(e)  The  amount  of  water  contained  in  a  substance  may 
be  determined  by  heating  in  a  drying  oven  to  105°  C.  for 
several  hours. 

After  discussion  in  the  class  room,  record  the  results 
obtained  by  the  different  students  as  follows: 

FOOD  FAT  SUGAR  STARCH  PROTEID         MINERAL        WATER 

Potato      None     None      Much      Little      Little      Much 

Clothing.  How  could  you  tell  the  difference  be- 
tween linen  or  cotton  on  the  one  hand  and  silk  or  wool 
on  the  other  by  burning  each  ?  Boil  a  little  cotton  cloth, 


EXPERIMENTS  :  >01 

all  wool,  and  a  mixed  wool  and  cotton  goods  one  aftei 
another  for  5  minutes  in  NaOH  solution.  What  is  the 
result.  Outline  another  method  of  distinguishing  be- 
tween wool  and  cotton. 

EXP.  54.    THE   HALOGEN  GROUP 

Materials.  Powdered  fluorspar,  calcium  fluorid,  CaF2. 
Salt,  NaCl.  Potassium  bromid,  KBr.  Potassium  iodid, 
KI.  Cone.  H2SO4.  Manganese  dioxid,  MnO2.  Paraffin. 

Apparatus.     Test  tubes.     Lead  dish.     Glass  plate. 

Procedure,     (a)  Hydrids  of  the  halogens. 

Place  1  g.  of  calcium  fluorid  in  a  test  tube,  add  3  ccm.  of 
cone.  H2SO4,  and  note  what  happens.  Warm  if  necessary 
to  hasten  the  reaction.  Treat  in  the  same  way  1  g.  each 
of  sodium  chlorid,  potassium  bromid,  and  potassium  iodid 
in  separate  test  tubes.  Blow  across  the  mouth  of  each 
tube.  In  each  case  what  causes  the  fuming?  Hold  blue 
litmus  in  the  fumes.  What  similarities  do  you  observe 
in  the  four  reactions  ?  Write  equations  showing  what  is 
formed  in  each  case. 

Does  the  mixture  in  any  of  the  tubes  become  colored  ? 
If  so,  what  colors  are  produced  and  which  one  changes 
most  quickly?  This  change  is  due  to  oxidation  of  the 
hydrogen  compound  first  formed  by  air  or  H2SO4.  To 
increase  this  effect,  add  a  pinch  of  manganese  dioxid  to 
each  test  tube  and  note  what  happens  in  each  case.  To 
prevent  fumes  getting  into  the  room,  wash  out  the  test 
tubes  as  soon  as  the  results  are  noted. 

Tabulate  your  results  as  follows  : 

COMPOUND  OXIDIZED  BY  AIR  OXIDIZED  BY  MnOj  STABILITY 

HF  Not  at  all  Not  at  all  Greatest 

HC1 

HBr 

HI 


102        IABOP.ATORY  MANUAL  IN  CHEMISTRY 

Hydrogen  fluorid  is  not  affected  by  the  most  vigorous 
oxidizing  agents.  Hydrogen  chlorid  is  oxidized  by  strong 
oxidizing  agents,  hydrogen  bromid  by  mild  oxidizing 
agents,  and  hydrogen  iodid  is  readily  oxidized  even  by 
the  air.  Write  equations  indicating  the  products  formed 
in  each  case. 

(5)  Etching  glass  ~by  hydrofluoric  acid. 

1.  Put  a  drop  of   cone.    H2SO4  on   a   piece   of  glass, 
sprinkle  into  it  a  pinch  of  powdered  fluorspar,  and  after 
some  minutes  note  the  action  of  the  liberated  hydrofluoric 
acid  on  the  glass. 

2.  Warm  a  glass  plate  about  10  cm.  square  and  cover 
one  side  of  it  with  a  thin  coating  of  paraffin.     Through 
this  wax,  when  cold,  scratch   letters  or  figures  with   a 
blunt    instrument,    taking    care   that  the  lines  are    not 

too  fine,  and  that  the  wax  is 
removed  through  to  the  glass. 
In  a  lead  dish  mix  about  5  g.  of 
powdered  fluorspar  with  enough 
cone.  H2SO4  to  make  a  thin 
paste,  lay  the  glass  plate  face 

down  on  the  dish  (see  Fig.  34),  and  allow  the  exposed 
places  to  be  acted  upon  for  24  hours  by  the  fumes  of 
hydrofluoric  acid. 

Scrape  off  the  wax  as  much  as  possible,  removing  the 
last  of  it  with  a  cloth  moistened  with  alcohol  or  benzine 
(Avoid  flames  !)  and  note  how  the  glass  is  etched. 

EXP.  55.    BROMIN 

Materials.  Bromin  water  (Br2)  containing  a  little 
liquid  bromin  at  the  bottom  of  the  bottle.  Chloroform,* 

*  Carbon  disulfid,  CS2,  may  be  substituted  for  chloroform,  though  it 
should  be  distilled  to  render  it  colorless.  Carbon  disulfid  must  be  kept 
away  from  all  flames. 


EXPERIMENTS  103 

CHClg.  Alcohol,  C2H6OH.  Colored  calico.  Potassium 
bromid  (KBr)  solution.  Chlorin  water,  C12. 

Apparatus.     Test  tubes. 

Procedure,  (a)  Examine  bromin  water  and  state  the 
properties  of  the  liquid  bromin  at  the  bottom  of  the  bottle. 
Does  bromin  appear  to  be  considerably  soluble  in  water? 
Cautiously  smell  of  the  solution  but  avoid  inhaling  much 
of  the  vapor,  as  bromin  attacks  the  membranes  of  the  eyes, 
nose,  and  throat  even  more  than  chlorin  does.  Inhaling 
the  fumes  from  a  handkerchief  moistened  with  alcohol 
will  partially  overcome  the  effects. 

Allow  a  piece  of  colored  calico  to  lie  in  bromin  water 
for  some  time.  Do  you  note  any  bleaching  action  similar 
to  chlorin? 

(5)  1.  To  10  com.  of  water  in  a  test  tube  add  about 
2  ccm.  of  chloroform,  shake  thoroughly,  then  allow  the  tube 
to  stand  for  a  few  moments.  Are  the  liquids  apparently 
soluble  in  each  other? 

Add  2  ccm.  of  bromin  water,  shake  again,  then  stand 
as  before.  Judging  by  the  color,  where  is  the  bromin, 
in  the  water  or  dissolved  in  the  chloroform? 

The  fact  that  bromin  will  collect  in  and  give  color  to 
chloroform  is  used  as  a  test  for  free  bromin. 

2.  To  see  whether  bromin  in  combination  with  other 
elements  will  give  this  test,  add  5  drops  of  KBr  solution 
to  10  ccm.  of  water  and  shake  with  chloroform  as  before. 
The  result  which  you  get  is  typical  of  all  compounds  con- 
taining bromin.     Make  a  general  statement  covering  your 
results. 

3.  To  the  mixture  used  in  (2)  add  5  ccm.  of  chlorin 
water  and  shake  again.     Result  ?     Do  you  get  a  test  for 
free  bromin  ?     What   must  have   set   the   bromin    free  ? 
Complete  the  following  equation  : 

—  KBr  +  Cl2->—  KC1  +  - 


104   LABORATORY  MANUAL  IN  CHEMISTRY 

Shake  chlorin  water  with  chloroform  and  see  if  chlorin 
possibly  gives  the  same  color  as  bromin. 

Another  method  of  liberating  bromin  was  used  in 
Exp.  54.  Make  a  general  statement  covering  this  method. 
Outline  a  method  of  preparing  bromin  from  KBr  based  on 
the  experiments  you  have  made. 

EXP.  56.     IODIN 

Materials.  lodin.  Alcohol.  Carbon  disulfid.  Chlo- 
roform.* Starch  paste. f  Potassium  iodid  (KI)  solution. 
Chlorin  water,  C12.  Bromin  water,  Br2.  Phosphorus. 

Apparatus.     Test  tubes.     Tile  or  brick.     Pincers. 

Procedure,  (a)  Examine  iodin  and  state  its  physical 
properties',  comparing  it  with  bromin  and  chlorin. 

Place  a  few  crystals  of  iodin  in  a  test  tube  and  heat 
gently,  noting  what  happens.  What  condenses  on  the 
cool  parts  of  the  glass  ?  Define  sublimation. 

Test  the  solubility  of  iodin  in  water,  alcohol,  carbon  di- 
sulfid and  chloroform,  noting  the  relative  degrees  of  solu- 
bility and  the  colors  produced. 

(b)  Add  a  drop  of  iodin  solution  to  some  very  dilute 
starch  paste  and  note  result.  This  is  used  as  a  test  for  free 
iodin.  What  other  use  have  you  made  of  this  same  re- 
action ?  To  see  whether  iodin  combined  with  other  ele- 
ments will  produce  the  same  color,  add  a  drop  of  KI 
solution  to  starch  paste.  Result  ? 

(V)  1.  Shake  2  ccm.  of  chloroform  with  10  ccm.  of  a 
water  solution  of  iodin.  Result  ?  This  procedure  is  used 
as  a  test  for  free  iodin. 

2.  Shake  similarly  2  ccm.  of  chloroform  with  20  ccm. 
of  water  containing  5  drops  of  KI  solution.  The  result  is 
typical  of  all  compounds  of  iodin.  Does  iodin  combined 
with  other  elements  give  the  iodin  test? 

*  See  footnote,  p.  102.  t  Prepared  as  directed,  p.  99. 


EXPERIMENTS  105 

3.  Pour  half  of  the  KI  solution  from  (2)  into  another 
test  tube,  add  2  ccm.  of  chloroform  and  5  ccm.  of  chlorin 
water  and  shake  thoroughly.     Result  ?     What  must  have 
set  the  iodin  free? 

4.  Add  to  the  remaining  KI  and  chloroform  mixture 
from  (2)  a  few  drops  of  bromin  water  and  shake.     Result  ? 
What  must  have  set  the  iodin  free  ? 

Write  equations  showing  the  action  of  chlorin  and 
bromin  on  potassium  iodid.  Write  an  equation  showing 
the  action  of  metals,  such  as  zinc,  on  acids.  Compare 
this  equation  with  the  two  preceding  equations  and  see 
if  you  can  note  any  similarity  in  the  reactions. 

(c?)  Put  a  little  iodin  on  a  tile  or  brick,  and  with  a 
glass  rod  or  pincers  press  gently  upon  it  a  small  piece 
of  phosphorus,  dried  between  filter  papers.  Result  ? 
How  did  chlorin  act  with  phosphorus  ?  Bromin  acts 
similarly.  Would  you  say  that  the  halogen  elements  are 
very  active  chemically  ? 

Outline  a  method  for  preparing  iodin  from  KI  based  on 
the  experiments  you  have  made. 

EXP.  57.    SULFUR 

Materials.  Sulfur.  Carbon  disulfid,  CS2.  Strip  of 
copper  foil  that  will  slip  into  a  test  tube.  Powdered 
iron.  Zinc  dust. 

Apparatus.  Test  tubes.  Test  tube  holder.  Watch 
glass  or  small  beaker.  Magnifying  glass.  15  cm.  filter 
paper.  Funnel.  Beaker  of  water. 

Procedure,     (a)  Physical  properties. 

1.  Examine  a  piece  of  ordinary  sulfur  and  note  its 
properties.  Shake  1  g.  with  3-5  ccm.  of  carbon  disulfid 
for  5-10  minutes,  pour  off  the  liquid  into  a  small  beaker 
or  watch  glass  and  allow  to  evaporate.  (Keep  carbon 


106        LABORATORY  MANUAL  IN  CHEMISTRY 

disulfid   away   from   flames !)      Make   a   sketch    of    the 
crystals  as  seen  under  a  lens.      This  is  rhombic  sulfur. 

2.  Fold  a  15  cm.  filter  paper  and  place  it  in  a  small 
funnel.     Fill  a  test  tube  about   half   full  of   sulfur  and 
melt  it  at  as  low  a  temperature  as  possible  by  holding  it 
over  a  flame  and  shaking  constantly.     Pour  the  melted 
sulfur  into  the  filter  paper  in  the  funnel   and  watch   it 
cool.     As  soon  as  a  few  crystals  have  formed,  pour  out 
upon  a  pan  the  sulfur  which  is  still  melted.     Open  the 
filter  paper,  examine  and  draw  the  crystals  of  monoclinic 
sulfur  thus  formed.      Are   they  clear  and  transparent? 
Keep  them  until  the  next  exercise  and  note  any  change. 

3.  Melt  a  half  test  tube  full  of  sulfur  as  before,  and  heat 
until  it   boils,  noting  the    changes  of  color  that   occur. 
From  time  to  time  during  the  heating,  tilt  the  test  tube 
and  note  the  changes  in  viscosity  indicated  by  the  readi- 
ness with  which  it  flows.     Note  the  color  of  sulfur  vapor 
and  pour  the  boiling  liquid  in  a  thin  stream  into  a  beaker 
of  water.     Where  the  sulfur  vapor  comes  in  contact  with 
the   cold   beaker   and   surface    of    the    water,   note    and 
describe  the  "  flowers  of  sulfur  "  which  form.     Examine 
the  properties  of  the  liquid  sulfur  suddenly  cooled  by  the 
water,  noting  its  color  and  hardness    and  whether  it  is 
elastic  or  brittle.     Keep  this  plastic  sulfur  until  the  next 
exercise  and  see  if  there  is  any  change  in  properties. 

State  in  detail  the  changes  in  properties  of  sulfur  ac- 
companying a  change  in  temperature. 

(6)    Chemical  properties. 

1.  Burn  a  piece  of  sulfur  and  cautiously  note  the  odor 
of  the  gas  produced.     State  in  chemical  terms  what  you 
mean  by  the  "  odor  of  burning  sulfur." 

2.  Heat  5  g.  of  sulfur  to  boiling  in  a  test  tube  until 
sulfur  vapor  fills  the  tube.     Warm  a  strip  of  copper  foil 


EXPERIMENTS  107 

in  the  burner  and  thrust  it  far  into  the  sulfur  vapor, 
noting  carefully  what  happens.  After  a  minute  or  two, 
withdraw  the  strip  and  examine  the  properties  of  the 
copper  sulfid  that  has  formed. 

3.  Recall  or  repeat  the  experiments  showing  how  iron 
and  zinc  combine  with  sulfur,  Exps.  2(d)  and  4(e). 

Would  you  say  that  sulfur  is  chemically  active  at  ordi- 
nary temperatures  ;  at  high  temperatures  ?  Write  equa- 
tions for  the  four  reactions  noted  above.  Compare  the 
action  of  sulfur  and  of  oxygen  on  these  metals. 

EXP.  58.    HYDROGEN  SULFID,  H2S 

Materials.  Iron  sulfid,  FeS.  Cone.  HC1.  Hydrogen 
peroxid,  H2O2.  Bromin  water.  Solutions  of  copper  sul- 
fate,  CuSO4;  arsenic  chlorid,  AsCl3* ;  antimony  chlorid, 
SbCl3 ;  stannous  chlorid,  SnCl2 ;  zinc  sulfate,  ZnSO4. 

Apparatus.  A  generator  such  as  was  used  in  preparing 
hydrogen,  Fig.  13,  but  the  gas  must  be  collected  by 
downward  displacement  and  not  over  water.  Glass  rod 
or  piece  of  porcelain.  Test  tubes.  Strip  of  copper. 
Silver  coin  (dime). 

CAUTION  :  Hydrogen  sulfid  is  a  poisonous  gas,  the  first 
effects  being  dizziness  and  headache.  Avoid  breathing 
it.  As  an  antidote  inhale  chlorin  from  a  handkerchief 
on  which  chlorin  water  has  been  sprinkled ;  or  add  HC1 
to  a  solution  of  "  chloride  of  lime  "  and  inhale  the  fumes. 

Procedure,  (a)  Preparation.  Fit  up  the  generator  as 
shown  in  Fig.  13.  Put  10-20  g.  of  iron  sulfid  in  the 
bottle  and  through  the  thistle  tube  add  about  25  ccm. 
of  cone.  HC1,  diluted  with  an  equal  volume  of  water. 
Allow  the  gas  to  bubble  into  100  ccm.  of  water  in  a 
beaker  until  the  water  smells  strongly  of  hydrogen  sulfid  ; 
*  Made  by  dissolving  As2O3  in  HC1. 


108        LABORATORY  MANUAL  IN   CHEMISTRY 

then  collect  2-3  bottles  by  downward  displacement. 
Add  cone.  HC1  through  the  thistle  tube  if  necessary  to 
hasten  the  action.  Complete  the  equation : 

FeS  +  —  HC1  ->  H2S  + . 

(6)  Physical  properties. 

Note  the  color,  odor,  and  taste  of  hydrogen  sulfid.  Is 
it  soluble  in  water  ?  (Smell  of  the  water  into  which  the 
gas  has  been  passing  before  answering  this  question.) 

Test  the  action  of  hydrogen  sulfid  water  on  blue  litmus 
paper  and  explain. 

(tf)    Chemical  properties. 

1.  Does  hydrogen  sulfid  support  combustion?     Does  it 
burn  ?     Light  the  gas  as  it  escapes  from  the  generator  and 
cautiously  smell  the  fumes.     What  is  one  product  of  com- 
bustion of  H2S  ?     Hold  a  cold  glass  rod  or  piece  of  porce- 
lain in  the  flame.     What  deposits  on  it?     Where  did  it 
come  from?     Why  do  you  get  no  deposit  when  the  gas 
burns  freely?     Compare  the  formation  of  a  deposit  here 
with  the  deposit  of  soot  in  an  ordinary  flame. 

2.  Add  a  few  drops  of  hydrogen  peroxid  to  10  ccm.  of 
H2S  water.     Explain  what  happens.     Is  H2S  an  oxidizing 
or  a  reducing  agent?     Complete  the  equation: 

H202  4-  H2S  ->  S  +  - 

3.  Add  a  few  drops  of  bromin  water  to  10  ccm.  of  H2S 
water  and  explain  what  happens.     All  the  other  halogen 
elements  will  act  similarly.     Complete  the  equation  : 

Br2  +  H2S  ->  S  + 

4.  Add  to  10  ccm.  of  H2S  water  a  few  drops  of  copper 
sulfate  solution  and  describe  what  happens.     In  a  similar 
way   add    arsenic    chlorid,    antimony    chlorid,    stannous 


EXPERIMENTS  109 

chlorid,  and  zinc  sulfate,  to  separate  portions  of  H2S  water. 
Describe  the  sulfids  formed  and  complete  the  equations  : 

CuSO4  +  H2S  ->  CuS  +  - 

—  AsCl3  +  —  H2S  -+  As2S3  +  - 

—  SbCl3  +  —  H2S  ->-  Sb2S3  +  - 

SnCl2  +  H2S  ->  SnS  +  - 
ZnSO4  +  H2S  ->  ZnS  H  -- 

5.    Hold  a  strip  of  copper  and  a  silver  coin  in  H2S  water 
and  note  the  effect.     Complete  the  equations  : 

Cu  +  HS  ->•  CuS  +  - 


No  considerable  action  of  this  kind  takes  place  except 
when  an  oxidizing  agent  (such  as  air)  is  present  to  com- 
bine with  the  nascent  hydrogen  as  it  is  liberated.  This 
action  is  mainly  responsible  for  the  tarnishing  of  silver. 

The  odor  of  hydrogen  sulfid  and  the  blackening  of  silver 
caused  by  its  solutions  are  tests  for  hydrogen  sulfid. 

EXP.  59.   SULFUR  DIOXID,  S02,  AND  SULFUROUS  ACID,  H2S03 

Materials.  Sulfur.  Wooden  splint.  Flowers,  or  piece 
of  calico.  Solutions  of  potassium  permanganate,  KMnO4; 
sodium  sulfite,  Na2SO3;  barium  chlorid,  BaCl2.  Litmus 
paper.  HC1.  NaOH.  Charcoal  or  copper.  Cone.  H2SO4. 

Apparatus.  Combustion  spoon.  Wide  mouth  bottle. 
Oxygen  generator  as  shown  in  Fig.  9  without  the  pneu- 
matic trough. 

Procedure. 

(a)  Preparation  ly  oxidation  of  sulfur. 

1.  Place  a  piece  of  sulfur  in  a  combustion  spoon,  ignite 
it  and  lower  it  into  a  wide  mouth  bottle.  Cover  the 
bottle  and  allow  the  sulfur  to  burn  until  the  flam'e  is 


110   LABORATORY  MANUAL  IN  CHEMISTRY 

extinguished.     Note  the  color,  odor,  and  taste  of  sulfm 
dioxid.     Will  it  burn  or  support  ordinary  combustion  ? 

Prepare  another  bottle  of  sulfur  dioxid  in  a  similar 
way.  Moisten  a  flower  or  piece  of  calico,  and  allow  it  to 
stand  in  the  sulfur  dioxid  for  some  time.  What  seems 
to  be  the  action  of  sulfur  dioxid  on  coloring  matter  ? 

2.  Pour  10-20  com.  of  water  into  a  bottle  and  shake 
it  about  so  that  the  bottle  is  wet  all  over.     Burn  sulfur 
above  the  water  in  the  bottle  as  before,  and  shake  so  that 
the  gas  produced  may  be  absorbed.     Pour  the  water  from 
the  bottle  and  smell  of  it.     Is  sulfur   dioxid  soluble  in 
water  ?     Test  the  water  with  blue  litmus  paper,  noting 
the  first  and  also  the  latter  effects.     Is  sulfur  dioxid  an 
acid   anhydrid?     Compare   the  following   equation  with 
the  action  of  carbon  dioxid  on  water. 

SO2  +  H2O  ->  H2SO3,  sulfurous  acid. 

3.  Add  NaOH  solution,  drop  by  drop,  to  the  sulfurous 
acid  solution  until  it  turns  litmus  paper  blue.     Does  the 
solution  smell  of   sulfur  dioxid  any  longer  ?     Complete 
the  equation  and  name  the  product  formed. 

H2S03  +  —  NaOH->Na2S03+ 

(5)  Preparation  by  reduction  of  sulfuric  acid,  H2SO4. 

1.  Fit  up  a  test  tube  with  an  outlet  and  delivery  tube 
as  shown  in  Fig.  9.     Fill  the  test  tube  one  eighth  full  of 
pieces  of  charcoal  or  copper,  and  add  10  ccm.  of   cone. 
H2SO4.     Suspend  the  apparatus  from  a  ring  stand   and 
heat   with    a    small    flame    as    the    gas   is    evolved.      If 
white  fumes  appear  above  the  liquid,  moderate  the  heat 
immediately. 

2.  Repeat  the  experiments  of  («)  sufficiently  to  assure 
yourself  that  the  same  gas  is  produced  in  (6)  as  in  (V). 

3.  Allow  the  gas  to  bubble  into  about  10  ccm.  of  water 


EXPERIMENTS  111 

in  a  test  tube  until  it  smells  strongly  of  sulfur  dioxid.      Use 
this  solution  for  (<?).     Complete  the  following  equations: 

H2S04  +  C->CO  +  --  >  -  •  +  - 
H2S04  +  Cu->CuO  +  -  ->  --  +  - 

(c)  The  odor  of  sulfur  dioxid  and  the  fact  that  it  will 
bleach  potassium  permanganate  are  used  as  tests  for  sulfur 
dioxid  and  sulfurous  acid. 

1.  Test  part  of  the  solution  obtained  in  (6)  by  adding 
a  few  drops  of  potassium  permanganate  solution*     What 
happens  ?     Do  you  get  a  test  for  SO2  and  H2SO3  ? 

2.  To  a  solution  of  sodium  sulfite,  add  HC1  and  note 
the  odor;  then  add  KMnO4  as  in  (1).     Do  you  get  the 
same  test  ?     Why  is  it  necessary  to  add  HC1  in  (2)  but 
not  in  (1)  ? 

3.  Add  barium  chlorid  and  HC1  to  (1)  and  (2).     The 
formation  of  a  white  precipitate  is  a  test  for  sulfates.     Did 
you  get  the  test  ? 

Permanganates  are  substances  very  rich  in  oxygen 
which  is  liberated  readily  and  oxidizes  sulfurous  acid. 
Complete  the  equation: 


H2S03  +  0->- 

EXP.   60.     SULFUR    TRIOXID,    S03,    AND    SULFURIC    ACID, 

H2S04 

Instructor's  Experiment 

Materials.  Scraps  of  platinum.  Cone.  HNO3and  HC1. 
Asbestos.  Cone,  solution  of  sulfur  dioxid.  Barium 
chlorid  (BaCl2)  solution. 

Apparatus.  A  2-liter  bottle  fitted  with  inlet  and  exit 
tube  as  used  in  Exp.  47,  connected  with  a  wash  bottle 
which  is  connected  with  a  glass  tube  about  30  cm.  long 
filled  with  asbestos  containing  finely  divided  platinum. 
Test  tube.  Porcelain  crucible.  Pipestem  triangle. 


112        LABORATORY  MANUAL  IN  CHEMISTRY 

Procedure.  Dissolve  0.5-1  g.  of  old  platinum  foil  or 
wire  in  aqua  regia,  evaporate  to  2-3  ccm.,  then  add  about 
10  com.  of  water.  Shred  some  asbestos  board,  soak  the 
shreds  in  the  platinum  solution  just  prepared,  and 
heat  to  redness  in  a  porcelain  crucible  or  dish.  By 
this  treatment  the  platinum  chlorid  is  decomposed, 
leaving  finely  divided  platinum  deposited  throughout  the 
asbestos. 

Set  up  the  apparatus  as  directed  above,  connecting  the 
inlet  tube  of  the  large  bottle  to  the  water  tap,  and  the 
outlet  tube  to  the  wash  bottle  which  contains  a  strong 
solution  of  sulfur  dioxid  in  water.  Loosely  fill  the  center 
third  of  the  glass  tube  with  the  platinized  asbestos,  sup- 
port it  on  a  ring  stand,  and  connect  it  to  the  exit  tube  of 
the  wash  bottle.  Arrange  the  apparatus  so  that  when 
water  enters  the  large  bottle,  air  will  be  forced  through 
the  solution  in  the  wash  bottle  and,  mixed  with  sulfur 
dioxid,  will  pass  over  the  platinum.  Regulate  the  stream 
of  water  so  that  about  one  bubble  a  second  passes  through 
the  wash  bottle.  Note  that  no  interaction  between  the 
sulfur  dioxid  and  oxygen  takes  place  at  ordinary  tempera- 
ture. When  the  tube  is  moderately  heated,  sulfur  trioxid 
is  formed.  State  what  you  observe.  Rinse  out  a  test 
tube  with  water  and  slip  it  over  the  end  of  the  tube  con- 
taining the  platinum  so  that  the  fumes  may  come  in  con- 
tact with  the  moisture  on  the  sides  of  the  tube.  After  a 
few  moments  rinse  out  the  test  tube  with  water  and  test 
the  solution  for  sulf uric  acid. 

EXP.   61.    PHOSPHORUS 

Materials.  Yellow  and  red  phosphorus.  Phosphorus 
pentoxid,  P2O5.  HC1.  Cone.  HNO8.  Solution  of  ammo- 
nium molybdate,  (NH4)2MoO4.  Commercial  fertilizers. 
Ferrous  sulfate,  FeSO4.  Cone.  H2SO4.  NaOH. 


EXPERIMENTS  113 

Apparatus.     Tile  or  brick.     Large   beaker.     Blue   lit 
mus  paper.     Glass  rod.     Cobalt  glass.     Platinum  wire. 

Procedure.  (#)  Note  the  physical  difference  between 
yellow  (observe  the  cautions  given  on  p.  15)  and  red 
phosphorus.  Place  a  little  of  each  upon  a  tile  or  brick 
and  touch  with  a  warm  glass  rod.  What  happens  ?  Heat 
the  glass  rod  and  try  to  ignite  the  red  phosphorus.  If 
you  do  not  succeed,  ignite  it  with  a  burner.  Compare  the 
way  red  and  yellow  phosphorus  take  fire  and  note  the 
product  formed  in  each  case. 

(5)  Dry  a  piece  of  phosphorus  about  the  size  of  a  pea, 
and  place  it  upon  a  tile  or  brick.  Ignite  it,  cover  with  a 
large  beaker  and  allow  to  stand  until  the  white  "  smoke  " 
has  settled.  What  is  the  "  smoke  "  ?  Describe  it. 

Press  a  moistened  piece  of  blue  litmus  paper  upon  some 
of  the  deposit.  Explain  what  happens.  Allow  the  de- 
posit to  stand  in  the  air  for  about  an  hour  and  note  what 
happens  ;  test  it  now  with  a  piece  of  dry  blue  litmus  paper 
and  explain  why  phosphoric  pentoxid  is  one  of  the  best  dry- 
ing agents.  Complete  the  equation  : 


(c)  Place  about  1  g.  of  phosphorus  pentoxid  in  a  test 
tube  and  add  a  few  drops  of  water.  Is  the  combination 
with  the  water  vigorous  or  mild  ?  Add  10  ccm.  of  water 
and  boil  for  5  minutes.  Add  one  drop  of  this  phosphoric 
acid  solution  to  5  ccm.  of  ammonium  molybdate  solution 
to  which  a  few  drops  of  cone.  HNO3  have  been  added. 
The  formation  of  a  yellow  precipitate  on  standing  5-10 
minutes  is  a  test  for  phosphates. 

(jot)  To  1  g.  of  commercial  fertilizer  add  10  ccm.  of 
water  and  a  few  drops  of  HC1,  heat  to  boiling  and  filter. 
Test  the  solution  for  salts  of  phosphoric  and  nitric 
(p.  72)  acids  and  of  ammonium  (p.  78)  and  potassium 


114        LABORATORY  MANUAL   IN   CHEMISTRY 


(p.  126).     Does  tliis  fertilizer  contain  all  the  foods  neces 
sary  for  a  plant  ? 

EXP.  62.     PHOSPHIN,  PH3 

Instructor's  Experiment 

Materials.    Solid  NaOH  or  KOH.    Yellow  phosphorus. 

Apparatus.     As  shown  in  Fig.  35. 

Procedure.     Put  about  50  g.  of  solid  NaOH  or  KOH, 

200  ccm.  of  water  and  2—3  pieces  of  phosphorus  about  the 

size  of  a  pea  in  a  quarter  or  half  liter  flask  and  set  up  the 

apparatus  as  shown  in 
Fig.  35.  Connect  the 
inlet  tube  of  the  flask 
with  the  gas  pipe  and 
allow  gas  to  flow  at 
full  head  into  the  flask 
for  a  minute  until  the 
air  is  replaced ;  then 
turn  down  the  gas  so 
that  about  1  bubble  in 
5  seconds  issues  from 
the  exit  tube.  Heat 
up  the  solution  in  the 
flask  until  it  nearly  reaches  the  boiling  point,  and  main- 
tain this  temperature  by  a  small  flame.  Phosphin  and 
other  hydrids  of  phosphorus  will  be  generated  and  escape 
through  the  water  into  the  air.  Describe  what  happens. 
What  can  you  say  about  the  kindling  temperature  of 
some  of  the  gases  formed  ?  What  difference  do  you 
notice  between  PH,  and  NH«?  What  is  the  "smoke" 

o  o 

formed  by  burning  PH8?  Why  is  it  necessary  to  remove 
the  air  from  the  flask  ?  What  would  happen  if  air  got 
into  the  flask? 


FIG.  35. 


EXPERIMENTS  115 

Before  taking  the  apparatus  apart,  allow  the  liquid  to 
cool  and  sweep  out  all  phosphids  by  turning  on  the  illu- 
minating gas  full  head  for  a  moment.  Pour  out  the 
solution,  wash  any  remaining  phosphorus  with  water  and 
replace  it  in  the  phosphorus  bottle. 

EXP.   63.    ARSIN,  AsH3,  AND  STIBIN,  SbH3 

Instructor's  Experiment 

Materials,  l^inc.  HC1.  Solutions  of  any  arsenic  com- 
pound, of  any  antimony  compound,  and  of  "  chloride  of 
lime." 

Apparatus.  2  hydrogen  generators.  2  clay  pipe  stem 
jets  for  burning  the  gas.  3  porcelain  plates  or  evaporat- 
ing dishes. 

Procedure.  Start  both  generators  and  ascertain  that  all 
air  has  been  driven  from  each  apparatus  by  testing  the 
purity  of  the  gas  as  directed  on  page  36.  When  the  gas 
collected  burns  quietly,  replace  the  delivery  tube  with  the 
pipe  stem  and  ignite  the  hydrogen  as  it  issues.  When  the 
hydrogen  burns  quietly,  introduce  into  one  generator 
through  the  thistle  tube  a  few  drops  of  any  arsenic  com- 
pound and  into  tho  other  the  same  amount  of  any  antimony 
compound.  Describe  the  changes  in  the  flames. 

Any  soluble  compound  of  arsenic  or  antimony  is  re- 
duced by  the  nascent  hydrogen  to  arsin  and  stibin. 
Write  equations  for  this  change,  assuming  that  you 
started  with  AsCL  and  SbCL. 

o  o 

Move  a  porcelain  plate  slowly  about  in  the  flame  in 
which  arsin  is  burning  and  describe  the  effect.  Get  a 
similar  deposit  from  the  stibin  flame  on  a  second  plate. 
This  procedure  is  known  as  the  Marsh  test  for  arsenic  and 
antirt^ony.  On  a  third  plate  trace  the  symbol  Sb  by  means 
of  the  stibin  flame  and  then  obliterate  it  by  means  of  the 
deposit  from  the  arsin  flame. 


116        LABORATORY  MANUAL  IN   CHEMISTRY 

Treat  all  three  plates  with  "  chloride  of  lime  "  solution 
and  state  the  results. 

What  differences  do  you  notice  between  AsH3  and 
SbH3  on  the  one  hand  and  NH3  on  the  other?  Write 
equations  showing  what  is  formed  when  arsin  and  stibin 
burn.  As2O3  and  Sb2O3  are  white  solids ;  do  you  get  any 
evidence  of  them  ?  When  the  flame  is  cooled,  elementary 
arsenic  or  antimony  is  deposited.  Compare  with  the  de- 
posit of  sulfur  from  burning  H2S  and  of  carbon  from  H4C 
and  other  hydrocarbons. 

The  deposit  of  arsenic  and  antimony  cannot  be  distin- 
guished with  certainty  except  by  chemical  means.  Ar- 
senic is  readily  dissolved  in  hypochlorites,  being  oxidized 
to  arsenic  pentoxid,  which  unites  with  water  to  form  ar- 
senic acid,  H3AsO4.  Antimony  is  not  easily  oxidized  by 
this  reagent,  hence  remains  on  the  plate.  Complete  the 
equations  and  compare  with  phosphoric  acid  (p.  113). 

_  As  +  —  O  -> 

As2°s  +  —  H2°  -*  —  H3  AsO4 

EXP.   64.     ELEMENTS  THAT  ACT  BOTH  AS  ACID- 
FORMERS  AND  BASE-FORMERS 

Materials.  Solutions  of  lead  nitrate,  Pb(NO3)2 ;  sodium 
carbonate,  Na2CO3;  sodium  sulfate,  Na2SO4;  potassium 
chromate,  K2CrO4 ;  stannous  chloride,  SnCl2 ;  zinc  sul- 
fate, ZnSO4 ;  aluminum  sulfate,  A12(SO4)3 ;  antimony 
chlorid,  SbCl3.  Arsenic  oxid,  As2O3.  Bits  of  tin,  zinc, 
and  aluminum.  NaOH.  KOH.  NH4OH.  HC1. 

Procedure,    (a)  Lead  as  a  base-former. 

Dilute  10  ccm.  of  lead  nitrate  solution  to  50  ccm.  with 
water.  To  5  ccm.  portions  of  this  solution  add  a  few 
drops  of  the  reagents  specified  :  (1)  NaOH  ;  (2)  Na2CO3  ; 
(3)  Na2SO4;  (4)  K2CrO4.  Note  the  result  in  each  case. 


EXPERIMENTS  117 

Write  equations  and  name  each  lead  compound  formed. 
What  uses  are  made  of  any  of  these  compounds  ?  Acting 
as  a  base-former,  lead  unites  with  what  kind  of  radicals  ? 

(5)  Lead  as  an  acid-former. 

1.  To  5  ccm.  of  your  lead  nitrate  solution  add  NaOH 
until  the  precipitate,  first  formed,  redissolves.    Write  equa- 
tions showing  what  lead  compound  you  now  have  in  solu- 
tion.    Name  it.     Test  this  solution  with  a  drop  of  each 
of  the  reagents  used  in  (a).     Do  you  get  any  of  these 
indications  of  the  presence  of  lead  ?     Why  not  ?     Lead  as 
an  acid-former  unites  with  what  kind  of  elements  ? 

2.  Use  KOH  as  in  (1).     Does  it  act  similarly  ? 

3.  Use  NH4OH  as  in  (1).     Does  it  act  similarly  ? 
What  makes  lead  act  as  an  acid-former?     (NH4OH  is 

not  sufficiently  strong  as  a  base  to  cause  any  element  to 
act  as  an  acid-former.) 

(<?)  Tin,  zinc,  aluminum^  antimony,  and  arsenic  as  well  as 
lead  readily  act  both  as  base-formers  and  as  acid-formers. 

1.  Precipitate  the  hydroxid  of  one  of  the  elements  men- 
tioned above  and  note  that  it  will  dissolve  either  in  HC1 
or  in  NaOH.     Some  students  choose  one,  others  another 
element.     (For  arsenic  hydroxid  use  the  solid  As2O3.) 

2.  Heat  a  bit  of  tin,  zinc,  or  aluminum  with  NaOH  and 
note  that  it  will  dissolve  in  this  as  it  will  in  HC1,  hydro- 
gen being  liberated  in  both  instances.     Write  equations 
expressing  the  reaction. 

EXP.   65.    REDUCTION  OF  METALS   FROM  THEIR  ORES 

Materials.  Piece  of  wood  charcoal  or  thick  bark.  Some 
of  the  following  oxids;  As2O3,  Sb2O3,  Bi2O3,  CuO,  PbO, 
SnO2,  ZnO.  Anhydrous  sodium  carbonate,  Na2CO3. 

Apparatus.     Blowpipe  (made  in  Exp.  49  (<?)). 


118        LABORATORY  MANUAL  IN   CHEMISTRY 


Procedure.  Scrape  a  shallow  depression  in  the  surface 
of  the  charcoal  or  bark.  Put  in  it  about  1  g.  of  lead  oxid 
and  direct  upon  it  the  reducing  flame  of  the  blowpipe.  If 
the  material  blows  away,  place  a  little  Na2CO3  on  it  and 
moisten  with  a  drop  or  two  of  water.  Sodium  carbonate 
takes  no  part  in  the  reaction ;  it  melts  and  holds  the 
material  together  and  protects  it  somewhat  from  the  air. 
After  heating  for  a  short  time,  allow  to  cool.  What 
change  has  taken  place  in  the  lead  oxid  ?  How  was  this 
change  brought  about  ?  Did  the  charcoal  have  any  in- 
fluence in  the  reduction  ? 

There  is  a  coating  formed  on  the  charcoal  about  the  de- 
pression. Note  its  color  when  hot  and  when  cold.  Does 
it  resemble  lead  oxid  ?  Its  formation  is  due  to  the  fact 
that  a  little  metal  is  volatilized,  oxidized  by  the  air,  and 
deposited  on  the  charcoal. 

Repeat  the  above  with  2-3  of  the  other  oxids,  different 
students  using  different  oxids.  Tabulate  as  follows: 


COATING 

METAL 

OBTAINED 

B   P  OF  MKTAI 

Hot 

Cold 

READILY  OR  NOT 

As2O3 

Sb203 

Bi2O3 

CuO 

! 

PbO 

SnO2 

ZnO 

The  oxids  of  copper  and  tin  are  difficult  to  reduce  in 
this  way,  requiring  long,  steady  heating  and  probably 
mixing  with  powdered  charcoal.  After  cooling,  turn  the 
material  over  with  a  knife  and  look  for  these  metals  on  the 


EXPERIMENTS  119 

bottom.  Did  you  obtain  globules  of  metallic  arsenic  and 
zinc  ?  Did  you  obtain  heavy  coatings  in  these  cases  ? 
Note  the  boiling  points  of  these  metals  (see  text,  p.  407) 
and  see  if  you  can  explain  these  results. 

Blowpipe  tests  of  this  character  are  often  used  to  deter- 
mine what  metal  is  present  in  a  compound,  for  when 
heated  with  sodium  carbonate  on  charcoal,  most  compounds 
of  the  elements  listed  above  will  be  reduced  to  the  metals. 

EXP.  66.     BORIC  ACID,  H3B03,  AND   BORAX   BEAD   TESTS 

Materials.  Borax,  Na2B4O7.  Cone.  H2SO4.  HC1. 
NaOH.  Alcohol.  Asbestos  shreds.  Turmeric  paper. 
Some  solid  compound  of  cobalt,  manganese,  chromium,  and 
iron,  such  as  Co(NO3)2,  MnO2,  Cr2(SO4)3,  and  Fe2O3  or 
iron  rust. 

Apparatus.  Beaker  and  test  tubes.  Pincers.  Plati- 
num wire  about  5  cm.  long.  Short  glass  tube.  Blowpipe. 

Procedure,  (a)  Dissolve  by  heating  to  boiling  10  g.  of 
borax  in  25  ccm.  of  water.  Add  3  ccm.  of  cone.  H2SO4to 
an  equal  volume  of  water  and  mix  thoroughly  with  the  hot 
borax  solution.  Note  what  happens  on  cooling  and  de- 
scribe the  boric  acid  which  crystallizes.  Pour  the  mixture 
through  a  filter  and  wash  the  crystals.  Touch  to  the 
tongue.  Is  boric  acid  a  strong  acid  ?  Complete  the 
equation  : 

Na2B4O7  +  H2SO4  +  —  H2O->4  H8BOP  + 


31 

(£)  1.  Place  some  of  the  boric  acid  in  an  evaporating 
dish  and  add  3-5  ccm.  of  alcohol.  Set  fire  to  the  alcohol  and 
note  the  color  of  the  flame.  If  the  color  is  not  distinct, 
soak  a  shred  of  asbestos  in  the  mixture  and  heat  in  the 
hottest  part  of  a  Bunsen  flame.  This  green  flame  is  used 
as  a  test  for  boric  acid. 


120   LABORATORY  MANUAL  IN  CHEMISTRY 

2.  Dissolve  a  crystal  of  borax  in  a  little  water  and  set 
free  the  boric  acid  by  adding  a  little  HC1.  Dip  a  piece  of 
turmeric  paper  in  the  solution  and  dry  it  by  placing  it  on 
the  outside  of  a  beaker  or  test  tube  of  boiling  water,  where 
it  will  be  heated  to  100°  but  not  much  higher.  The  red 
color  which  appears  on  drying  is  a  test  for  borates.  (With 
dilute  solutions  it  may  be  necessary  to  wet  the  turmeric 
paper  and  dry  it  repeatedly  to  get  a  good  test.)  Moisten 
the  red  paper  with  an  alkali  and  note  the  change  of  color. 
Will  HC1  restore  the  color  ? 

(V)  Rotate  one  end  of  a  piece  of  glass  tubing  in  a 
Bunsen  flame  and  just  as  the  glass  is  running  together 
insert  a  platinum  wire  about  5  cm.  long  heated  red 
hot.  The  glass  tube  will  serve  as  a  handle  and  prevent 
loss  of  the  wire. 

Make  a  loop  in  the  end  of  the  platinum  wire  about. 
2-3  ram.  in  diameter  by  wrapping  the  wire  once  around 
the  point  of  a  lead  pencil.  Heat  the  loop  and  while 
hot  press  it  against  a  small  crystal  of  borax,  thus 
causing  it  to  adhere.  Heat  the  borax  in  the  hottest 
part  of  the  Bunsen  flame  or  better  in  the  flame  of  a 
blowpipe,  noting  how  it  swells  up  as  the  water  in  the 
crystals  boils  away.  Note  also  the  clear  bead  finally 
produced. 

While  this  bead  is  hot,  press  it  against  a  mere  trace  of 
a  cobalt  compound  and  heat  again.  Note  the  color 
produced. 

To  remove  the  bead,  heat  it  red  hot  and  shake  it  out  of 
the  loop  or  plunge  it  into  water,  thus  causing  it  to  disin- 
tegrate. Make  a  new  bead  and  see  that  it  is  colorless.  If 
not*  shake  out  again  and  start  anew. 

Make  similar  beads  containing  manganese,  chromium, 
and  iron  compounds.  Heat  all  the  beads  in  the  oxidizing 
flame  and  record  the  colors  produced. 


EXPERIMENTS  121 

EXP.    67.     ALUM  FROM  CLAY 

Materials.  Clay.  Cone.  H2SO4.  Potassium  carbon- 
ate, K2CO3.  NH4OH.  Solutions  of  cobalt  nitrate, 
Co(NO3)2,  and  alum,  KA1(SO4)2. 

Apparatus.  Evaporating  dish.  Beakers  and  funnel. 
Plaster  of  Paris  block  *  or  piece  of  charcoal  or  bark. 

Procedure,  (a)  Mix  thoroughly  50  g.  of  dry,  finely 
pulverized  clay  soil  with  30  ccm.  of  cone.  H2SO4  in  an 
evaporating  dish,  and  heat  for  20  minutes  (Hood)  over  a 
low  flame  to  such  a  temperature  that  white  "fumes  just 
begin  to  appear.  When  cool,  pour  the  mixture  into  a 
beaker,  add  100  ccm.  of  boiling  water,  stir  thoroughly, 
allow  to  settle,  and  while  still  hot  decant  the  liquid  as 
completely  as  possible  into  a  second  beaker.  Treat  the 
residue  in  the  same  way  with  50  ccm.  and  then  with 
30  ccm.  of  boiling  water.  Heat  the  combined  water  ex- 
tracts to  boiling,  and  add  slowly  with  constant  stirring, 
12  g.  of  solid  potassium  carbonate.  After  all  action  has 
ceased,  filter  the  boiling  liquid.  Evaporate  the  filtrate  to 
half  its  original  volume  and  set  aside  to  cool  until  the 
next  exercise.  Remove  the  crystals  obtained  and  dry 
them  between  filter  papers. 

More  crystals  may  be  obtained  by  further  concentra- 
tion of  the  remaining  liquid.  They  will  not  be  as  pure 
and  may  need  recrystallization  to  get  them  colorless. 

The  composition  of  clay  may  be  taken  as  HAlSiO4,  the 
reaction  on  heating  with  H2SO4  being  : 

2  HA18iO4  +  3  HaSO4->  A12(SO4)8  -f  —  SiO2-f  -  -  H2O 

In  the  preceding  equation  fill  in  the  numbers  necessary 
to  make  it  balance.  The  effervescence  produced  on  add- 

*  Mix  plaster  of  Paris  with  one  third  its  weight  of  water  and  pour 
it  upon  a  sheet  of  paper  laid  upon  the  desk.  When  it  has  partially 
hardened,  cut  it  into  pieces  about  10  x  2  cm.  and  allow  to  dry. 


122        LABORATORY  MANUAL  IN   CHEMISTRY 

ing  K2CO3  is  due  to  the  excess  of  H2SO4  not  used  in 
decomposing  the  clay.  Write  the  equation  for  the  forma- 
tion of  alum. 

(5)  Dilute  5  ccm.  of  alum  solution  with  10  ccm.  of 
water  and  add  NH4OH.  Notice  the  character  of  the 
aluminum  hydroxid  precipitated.  Heat  the  mixture  to 
boiling  and  filter.  Heat  some  of  the  precipitate  with  the 
blowpipe  upon  charcoal  or  plaster  of  Paris  and  note  the 
character  of  the  aluminum  oxid  formed.  Moisten  the  alu- 
minum oxid  with  a  drop  of  cobalt  nitrate  and  heat 
strongly  again.  A  blue  color  is  a  test  for  aluminum. 
(Zinc  gives  a  green  color  when  similarly  treated.) 

(c)  Shake  some  pulverized  clay  with  water  and  allow 
the  heavier  material  to  settle  out  for  ten  minutes.  With 
100  ccm.  of  the  turbid  water  mix  5  ccm.  of  alum  solution. 
Add  a  piece  of  litmus  paper  and  make  just  alkaline  with 
ammonium  hydroxid.  Note  the  time  it  takes  this  solution 
to  settle  clear  as  compared  with  some  of  the  water  that  has 
not  been  so  treated.  This  illustrates  a  method  for  making 
turbid  water  clear,  except  that  the  cheaper  calcium  hy- 
droxid is  used  instead  of  ammonium  hydroxid.  What 
causes  the  clay  to  settle  ? 

EXP.  68.     DYES  AND  MORDANTS 

Materials.  Pieces  of  white  cotton  cloth  about  2  by 
10  cm.  Cone.  HC1.  NH4OH.  Solution  of  Congo  Red 
containing  1  g.  of  dye,  1  g.  of  Na2CO3,  and  2  g.  of  Na2SO4 
in  each  100  ccm.  of  water.  Solution  of  alizarin  containing 
1  g.  of  dye  in  each  100  ccm.  of  water  and  enough  NH4OH 
to  make  it  go  into  solution.  Solution  of  aluminum  sulfate, 
A12(SO4)3.  Solution  of  cochineal  *  — boil  10  g.  in  100 
ccm.  of  water.  Extract  of  logwood  made  by  covering 
logwood  with  water  and  bringing  it  to  boiling.  Do  this 
four  times.  Reject  first  three  ;  keep  fourth. 
*  Cochineal  contains  carminic  acid. 


EXPERIMENTS  123 

Apparatus.     Evaporating  dish,  test  tubes,  and  beakers. 
Procedure,     (a)   To  remove  the  "  sizing  "  from  the  cloth. 

Add  5  ccm.  of  cone.  HC1  to  100  com.  of  water  in  a  beaker, 
place  3-5  pieces  of  cloth  in  this  solution,  and  heat  to  boil- 
ing; then  wash  the  cloth  thoroughly  in  running  water 
and  finally  dip  in  water  containing  a  few  drops  of  NH4OH. 

(5)  1.  Dilute  5  ccm.  of  the  Congo  Red  solution  to 
50  ccm.  with  water  in  an  evaporating  dish.  Keep  the 
solution  boiling  gently  and  immerse  a  piece  of  cloth  in  it 
for  3-5  minutes,  stirring  constantly.  Remove  the  cloth, 
wash  thoroughly,  dry  and  put  in  your  notebook.  Congo 
Red  dyes  cotton  without  a  mordant. 

2.  Dilute  5  ccm.  of  the  alizarin  solution  to  50  ccm.  with 
water.  Boil  a  piece  of  cloth  in  it ;  remove,  wash,  and  dry 
as  before.  Does  alizarin  dye  cotton  without  a  mordant  ? 

(V)  1.  Add  a  few  drops  of  NH4OH  to  5  ccm.  of  a  solu- 
tion of  aluminum  sulfate.  What  is  precipitated  ? 

2.  Pour  5  ccm.  of  your  alizarin  solution  into  a  test 
tube,  dilute  with  10  ccm.  of  water,  heat  to  boiling  and  add 
5  ccm.  of   aluminum    sulfate   solution.     If   a  precipitate 
does  -not  form  immediately  because  of  the  NH4OH  in  the 
alizarin  solution,  add  a  few  drops  of  NH4OH.     Allow  to 
stand  until  the  precipitate  settles.     Where  is  the  color,  in 
the  liquid  or  in  the  precipitate  ?     An  insoluble  compound 
formed  by  the  union  of  a  base  (or  an  acid)  with  a  dye  is 
called  a  lake. 

3.  Soak  a  piece  of  cloth  in  the  aluminum  sulfate  solution, 
squeeze  it  dry  and  attempt  to  dye  it  in  your  alizarin  solu- 
tion as  before.     Is  the  result  any  better  ?     Where  is  the 
lake  in  this  case  ?     Aluminum  hydroxid  acts  as  a  mordant 
for  alizarin;  also  for  other  dyes  including  logwood  and 
carminic  acid  (cochineal).     If  you  have  time,  try  one  of 
these  also. 


124        LABORATORY  MANUAL  IN  CHEMISTRY 

EXP.  69.    HARD  WATER  AND  HOW  TO  SOFTEN  IT 

Materials.  Soap  cut  into  pieces  about  the  size  of  a  pea. 
Solutions  of  calcium  sulfate,  CaSO4;  sodium  carbonate, 
Na2CO3;  borax,  Na2B4O7  ;  and  sodium  phosphate  to  which 
1  g.  of  NaOH  is  added  for  each  5  g.  of  Na2HPO4,  thus 
forming  Na3PO4.  Lime  water,  Ca(OH)2.  HC1.  NaOH. 
NH4OH.  Litmus  paper.  Several  different  kinds  of  wash- 
ing powders  or  "boiler  compounds."  Marble,  CaCO3. 
Ammonium  molybdate,  (NH4)2MoO4.  Turmeric  paper. 

Apparatus.     Carbon  dioxid  generator  (p.  85). 

Procedure,     (#)  Hard  waters. 

Dilute  40  ccm.  of  lime  water  with  60  ccm.  of  water,  pass 
in  carbon  dioxid  until  the  precipitate  first  formed  is  re- 
dissolved.  Write  equations  expressing  the  change  taking 
place.  What  substance  is  in  solution  ?  Call  this  No.  I. 

Add  20  ccm.  of  calcium  sulfate  solution  to  80  ccm.  of 
water.  Call  this  No.  II. 

1.  Take  half  a  test  tube  full  of  distilled  water,  add  a 
piece  of  soap,  cover  with  the  thumb,  and  shake,  noting  the 
readiness  with  which  a  lather  is  formed. 

2.  Treat  half  a  test  tube  of  No.  I  in  the  same  way. 
Does  it  lather  readily  ? 

3.  Treat  half  a  test  tube  of   No.  II  just  as  in    (2). 
Does  it  lather  readily  ? 

Solutions  I  and  II  are  typical  hard  waters.  Magnesium 
salts  act  similarly  to  calcium  salts  and  both  are  commonly 
present  in  water. 

4.  Remove  some  of  the  precipitate  ("scum  ")  appearing 
in  (2)  and  (3)  to  a  watch  glass  and  treat  with  2-3  ccm. 
of  water  and  5  drops  of  HC1.     The  precipitate  dissolves, 
but  a  new  one  (stearic  acid)  forms  immediately.     Scrape 
this  on  to  the  edge  of  the  watch  glass,  drain  off  the  liquid, 
wash  with  a  few  drops  of  water  and  add  5  drops  of  NaOH. 


EXPERIMENTS  125 

Does  the  precipitate  dissolve  ?     Stir  it  and  see  it  lather. 
What  is  in  the  solution  ?     What  is  the  "  scum  "  ? 

5.  Boil  half  a  test  tube  of  No.  I.     Do  you  note  any 
change  ?     Shake  with  soap  as  before.     Is  there  any  dif- 
ference now?     Explain  why.     Water  that  is  softened  by 
boiling  is  called  "  temporarily  hard  water." 

6.  Treat  half  a  test  tube  of  No.  II  as  in  (5),  answering 
the  same  questions.     What  is  the  difference  between  the 
two  hard  waters  ?       Water   not   softened   by  boiling  is 
called  "  permanently  hard  water." 

(6)    Chemical  methods  of  softening  hard  water. 

1.  Add  NH4OH  to  half  a  test  tube  of   I    until   red 
litmus  turns  blue.     Shake  with  soap   as   before.       Does 
NH4OH    soften   the    water?       In    softening    temporarily 
hard  water,  any  base    will  act   similarly.       Usually   the 
calculated  amount  of  lime,  the  cheapest  base,  is  added  to 
it.     Complete  the  equation  : 

CaH2(C03)2  -f  Ca(OH)2  -»-  - 

2.  Add  2-3  ccm.  of  sodium  carbonate  solution  to  half 
a  test  tube  of  either  I  or  II.     Do  you  note  any  change  ? 
Shake  with  soap.     Is  the  water  soft  ?     Write  equation. 

3.  Add  2-3  ccm.  of  borax  solution  as  in  (2).     Result? 

4.  Add  2-3  ccm.  of  sodium  phosphate  solution  as  in  (2) 
Result  ? 

(<?)  Analysis  of  washing  powders. 

Make  a  solution  of  the  powder,  or  "  boiler  compound," 
and  test  for  carbonates  (p.  86),  borates  (p.  120),  phosphates 
(p.  113),  and  ammonium  salts  (p.  78).  Test  also  for  soap 
by  acidifying  with  HC1  and  see  if  a  precipitate  of 
stearic  acid,  etc.  forms  (p.  97^.  What  does  the  powder 
contain  ?  Let  different  students  analyze  different  powders 
and  thus  find  out  what  is  on  the  local  markets. 


126        LABORATORY  MANUAL  IN   CHEMISTRY 

EXP.  70.     FLAME  TESTS  —  COLORED  FIRE 

Materials.  Solutions  of  the  chlorids  of  calcium  (CaCl2)v 
strontium  (8r012),  barium  (BaCl2),  potassium  (KC1),  and 
sodium  (NaCl).  Sugar.  Strontium  chlorate,  Sr(ClO3)2. 
Barium  chlorate,  Ba(ClO3)2.  HC1. 

Apparatus.  Mortar  and  pestle.  Tile  or  brick.  Plati- 
num wire.  Test  tubes.  Blue  cobalt  glass. 

Procedure,  (a)  Clean  your  platinum  wire  by  alter- 
nately dipping  in  HC1  and  heating  until  it  gives  no  color 
to  the  flame.  Then  dip  the  wire  in  a  solution  of  calcium 
chlorid,  and  note  the  color  given  to  the  flame. 

Clean  your  wire  between  each  test.  Note  and  record 
the  color  produced  by  chlorids  of  strontium,  barium,  potas- 
sium, and  sodium. 

Dip  your  wire  into  a  solution  of  sodium  chlorid  and 
then  of  potassium  chlorid,  and  note  which  of  the  two 
you  can  detect  in  the  flame.  Dip  the  wire  into  both 
solutions  again,  and  look  at  the  flame  through  a  piece 
of  blue  cobalt  glass.  Which  color  do  you  see  now? 
What  use  could  you  make  of  the  blue  cobalt  glass  ? 

Compounds  of  the  elements  mentioned  above,  when 
moistened  with  HC1,  generally  give  their  characteristic 
flame  tests. 

(b)  In  separate  mortars  *  pulverize  5  g.  of  cane  sugar 
and  an  equal  volume  of  strontium  chlorate.  Mix  thor- 
oughly on  a  "filter  paper  (Do  not  grind  together),  place 
on  a  tile  or  brick,  and  ignite  with  a  burner.  Why  does 
the  combustion  take  place  so  vigorously  ?  What  com- 
pound gives  color  to  the  flame  ? 

Mix  similarly  5  g.  of  sugar  with  an  equal  volume  of 
barium  chlorate  and  ignite. 

*  Three  students  should  work  together  on  (6),  one  powdering  the 
sugar,  one  the  strontium  chlorate,  and  one  the  barium  chlorate. 


EXPERIMENTS  127 

EXP.   71.     MANUFACTURE  OF  POTASSIUM  NITRATE 

Materials.  Sodium  nitrate,  NaNO3.  Potassium  chlorid, 
KC1.  Potassium  nitrate,  KNO3. 

Apparatus.  Beakers  and  test  tubes.  Cobalt  glass. 
Platinum  wire. 

Procedure.  Dissolve  by  heating  28  g.  of  NaNO3  in 
20  ccm.  of  water.  Put  25  g.  of  KC1  in  30  ccm.  of  water 
and  heat  to  boiling  ;  then  add  the  NaNO3  solution.  Con- 
tinue to  boil  the  mixture  until  its  volume  is  reduced 
nearly  one  third,  remove  from  the  gauze  and  allow  to 
settle ;  then  immediately  decant  the  clear  liquid  from  the 
crystals  as  completely  as  possible  into  another  beaker  and 
allow  it  to  crystallize  also. 

Wash  the  crystals  in  the  first  beaker  with  5  ccm.  of 
boiling  water  and  decant  the  washings.  Taste  the  sub- 
stance and  apply  the  flame  test.  What  is  it?  Write  an 
equation  indicating  how  it  was  formed. 

Cool  the  second  beaker,  if  possible  in  ice  water,  decant 
the  liquid  from  the  crystals,  dissolve  in  the  least  possible 
amount  of  boiling  water,  and  recrystallize.  Note  the 
form  of  the  crystals,  taste  them  and  apply  the  flame  test 
using  the  blue  glass.  Potassium  nitrate  crystallizes  in 
needles.  Taste  it.  What  is  the  second  substance  ob- 
tained in  this  experiment  ? 

Consult  the  text  (p.  64)  and  ascertain  which  of  the 
four  substances  present  in  the  solution  is  least  soluble  at 
100°  and  which  at  0°.  Which  is  most  likely  to  separate 
from  the  boiling  solution  therefore  ?  What  effect  on  the 
reaction  would  this  have  ?  Which  substance  is  most 
likely  to  separate  from  the  cold  solution?  State  two 
reasons  why.  Can  you  suggest  any  changes  in  this 
process  that  would  make  it  more  efficient  on  a  commercial 
seale  ? 


128        LABORATORY  MANUAL  IN  CHEMISTRY 

EXP.   72.    WASHING   SODA,  BAKING   SODA,   AND  BAKING 

POWDER 

Materials.  Washing  soda,  Na2CO3.  Baking  soda, 
HNaCO3.  Several  different  brands  of  baking  powder. 
Some  cleaning  compounds.  HC1.  NaOH.  NH4OH. 
Lime  water,  Ca(OH)2.  Solutions  of  iodin;  barium 
chlorid,  BaCl2;  ammonium  molybdate,  (NH4)2MoO4; 
cobalt  nitrate,  Co(NO3)2.  Marble,  CaCO3. 

Apparatus.  Carbon  dioxid  generator  (see  p.  85).  Test 
tubes.  Beakers.  Evaporating  dish. 

Procedure,     (a)    Washing  soda  and  baking  soda. 

1.  Touch  some  baking  soda  and  then  some  washing 
soda  to  the  tongue  and  try  to  distinguish  them  by  taste. 

2.  Moisten  the  hands  with  a  solution  of  washing  soda 
and  then  wash  them  in  water.     Is  washing  soda  a  good 
cleaning  agent  ?     It  is  the  principal  ingredient  in  most 
washing  and  cleaning  compounds.     Add  HC1  to  some  of 
them  and  see  if  they  do  not  effervesce. 

3.  Pass  carbon  dioxid  from  a  generator  into  2  g.  of 
washing  soda  in  10  ccm.  of  water.     Taste  the  solution 
resulting  after  the  liquid  is  apparently  saturated  with  gas. 
Is  the  product  baking  soda  ?     How  may  washing  soda  be 
converted  into  baking  soda  ? 

4.  Put  5  g.  of  baking  soda  into  a  test  tube  and  heat 
gently.     What   do   you   observe  ?     Put   5   ccm.   of   lime 
water  into  a  small  beaker  and  tilt  the  test  tube  so  that  if 
a  heavy  gas  is  liberated  by  the  baking  soda  it  may  pour 
into  the  beaker.    Shake  the  lime  water  frequently.     What 
inference  do  you  draw  from  the  result?     What  condenses 
on  the  cold  parts  of  the  test  tube  ?     Taste  the  product 
left  in  the  test  tube.     Is  it  washing  soda  ?     Write  an 
equation  expressing  the  change  of  baking  soda  into  wash- 
ing soda. 


EXPERIMENTS  129 

5.  To  get  an  idea  at  what  temperature  baking  soda  is 
converted  into  washing  soda,  put  5  g.  of  baking  soda  into 
10.  com.  of  water  and  heat  gently.  Is  gas  liberated  be- 
fore the  water  boils  ?  What  is  the  purpose  of  baking  soda 
in  making  bread  or  cake  ?  What  product  is  left  in  the 
bread  ?  See  if  you  can't  taste  it  in  "  soda  biscuits  "  or 
cake  made  with  soda. 

(5)  Baking  powder. 

1.  Examine  some  baking  powder  and  see  if  you  notice 
any  action  taking  place.  Pour  a  little  water  upon  it. 
What  happens?  Test  the  gas  with  lime  water.  What  is 
it  ?  What  causes  the  dough  to  begin  to  rise  as  soon  as  it 
is  mixed  ?  What  causes  it  to  rise  in  the  oven  ? 

Calculate  how  much  (a)  baking  soda  and  (6)  washing 
soda  will  be  necessary  to  liberate  100  ccm.  (standard  con- 
ditions) of  carbon  dioxid,  when  treated  with  HC1.  Write 
equations  showing  the  products  formed  in  each  of  these 
cases.  If  mixed  in  the  proper  proportions,  could  these 
mixtures  be  used  to  raise  bread?  Why  is  baking  soda 
always  used  as  a  leavening  agent  instead  of  washing  soda? 

(c)  Analysis  of  baking  powders. 

All  baking  powders  contain  baking  soda,  but  many  dif- 
ferent substances  are  used  to  unite  with  it  and  liberate 
the  gas,  such  as  an  acid  salt  of  tartaric,  phosphoric,  or 
sulfuric  acid.  Ammonium  carbonate  and  ammonium 
alum,  NH4A1(SO4)2,  are  sometimes  present,  and  starch 
is  frequently  added  to  prevent  the  ingredients  from  act- 
ing on  each  other. 

1.  Pour  25  ccm.  of  water  and  10  drops  of  cone.  HC1 
upon   10   g.    of   baking  powder,   shake   thoroughly,   then 
settle  and  decant  the  clear  liquid  through  a  filter. 

2.  Boil  the  residue  with  a  little  water,  cool  and  add  a 
drop  of  iodin  solution.     Do  you  get  a  test  for  starch  ? 


130        LABORATORY  MANUAL  IN  CHEMISTRY 

3.  Evaporate  5  com.  of  the  filtered  liquid  to  dry  ness  in 
an  evaporating  dish.  If  a  tartrate  is  present,  it  will  turn 
black  and  smell  like  burned  sugar. 

Test  a  few  drops  of  the  filtered  liquid  (4)  for  sulfates 
(p.  Ill),  and  (5)  for  phosphates  (p.  113). 

6.  Test  5  ccm.  for  ammonium  salts  (p.  78). 

7.  Make  5  ccm.  of  the  filtered  solution  alkaline  with 
NH4OH.    Is  gelatinous  aluminum  hydroxid  precipitated  ? 
If  you  are  in  any  doubt,  test  for  aluminum  in  the  precipi- 
tate by  the  cobalt  nitrate  test  (p.  122).     What  substances 
did  you  find  in  the  baking  powders? 

EXP.  73.  THE  REPLACEMENT  OF  ONE  METAL  BY 
ANOTHER 

Materials.  Solutions  of  zinc  sulfate,  ZnSO4;  copper 
sulfate,  CuSO4;  ferric  chlorid,  FeCl3;  mercuric  chlorid, 
HgCl2;  silver  nitrate,  AgNO3.  Zinc  strips.  Copper 
wire  or  strips.  Iron  nails.  Mercury.  Lead  acetate, 
Pb(C2H3O2)2.  Stannous  chlorid,  SnCl2.  Acetic  acid. 

Apparatus.  10  test  tubes.  Test  tube  rack  or  beakers 
to  hold  the  test  tubes.  2  large  beakers. 

Procedure,  (a)  Using  separate  test  tubes  put  the  fol- 
lowing metals  into  5  ccm.  of  a  solution  of  the  salts  indi- 
cated. In  each  case  record  whether  a  deposit  appears  on 
the  metal  and  what  it  seems  to  be,  rubbing  the  metal 
with  the  finger  in  2  and  5  to  get  evidence  on  this  point. 
In  5  and  6  what  does  the  blue  color  of  the  resulting  solu- 
tion indicate  ?  Write  equations  expressing  all  reactions. 

1.  Zn  in  CuSO4.  6.    Cu  in  AgNO3. 

2.  Zn  in  HgCl2.  7.    Cu  in  FeCl3. 

3.  FeinCuS04.  8.    Hg  in  AgNO3. 

4.  Fe  in  ZnSO4.  9.    Hg  in  ZnSO4. 

5.  Cu  in  HgCl2.  10.    Hg  in  CuSO4. 


EXPERIMENTS  131 

(6)  For  the  instructor. 

1.  Dissolve  50  g.  of  lead  acetate  in  250  ccm.  of  water, 
add  1-2  ccm.  of  acetic  acid  and  by  a  string  suspend  in  the 
solution  a  bunch  of  zinc  turnings  or  strips.      Allow  to 
stand  overnight  and  note  the  replacement  of  the  lead  by 
the  zinc. 

2.  Add  25  ccm.  of  cone.  HC1  to  500  ccm.  of  water  and 
dissolve  in  it  30  g.  of  stannous  chlorid.     In  a  similar  way 
allow  zinc  to  hang  in  the  solution  overnight.    Note  the  re- 
placement of  tin  by  zinc. 

From  the  experiments  you  have  seen,  arrange  the 
metals  in  the  order  in  which  they  stand  in  the  Potential 
or  Replacement  Series,  the  highest  coming  first. 

EXP.   74.    REACTIONS  OF  SILVER  SALTS  IN  PHO- 
TOGRAPHY 

Materials.  Solutions  of  silver  nitrate,  AgNO8  (2  g.  in 
each  100  ccm.);  of  potassium  bromid,  KBr  (4  g.  in  each 
100  ccm.);  of  "hypo,"  sodium  thiosulfate,  Na2S2O3  (125  g. 
in  500  ccm.).  Developer  made  as  follows:  2  g.  hydro- 
chinon,  8  g.  sodium  sulfite  crystals,  8  g.  sodium  carbonate 
crystals,  5  ccm.  of  oxalic  acid  solution  in  each  250-300 
ccm.  of  water. 

Apparatus.     Test  tubes.     Cork.     Black  paper. 

Procedure.  Clean  4  test  tubes  thoroughly.  Wrap 
black  paper  about  one  and  fit  it  with  a  clean  cork.  Put 
exactly  5  ccm.  of  AgNO3  solution  and  10  ccm.  of  water 
into  this  test  tube.  Measure  out  exactly  5  ccm.  of  potas- 
sium bromid  into  another.  Carry  all  of  the  test  tubes 
into  a  room  darkened  as  much  as  possible.  In  the  dark 
add  the  KBr  to  the  AgNO3,  cork  the  tube  and  invert  once 
or  twice  but  do  not  shake  it.  Pour  one  third  of  the  mix- 
ture into  each  of  the  two  clean  test  tubes.  Keep  one  third 


132        LABORATORY  MANUAL  IN  CHEMISTRY 

in  the  test  tube  wrapped  in  black  paper  in  the  dark 
room.  What  is  the  precipitated  material  in  the  test 
tubes  ?  Write  an  equation  for  its  formation. 

1.  Add  10  ccm.  of  hypo  to  one  portion  of  silver  bromid. 
What  happens  ?    What  is  the  use  of  hypo  in  photography  ? 

2.  Add  5  ccm.  of  developer  to  the  silver  bromid  in  the 
dark   room.      After  2-3  minutes  add  10  ccm.  of  hypo, 
shake,  bring  to  the  light,  and  remove  black  paper.     There 
should  be  no  difference  between  the  results  in  (1)  and 
(2)   if   the   latter  has  not  been    exposed    to    the    light. 
A  developer  is  a  reducing  agent  not  strong   enough  to 
reduce   silver   salts  unless   they  have   been   exposed   to 
light. 

3.  Expose  the  third  portion  of  silver  bromid  2-3  min- 
utes to  direct  sunlight,  shaking  the  tube  to  expose  all 
portions  equally.     Add  5  ccm.   of  developer.      Explain 
what  happens.     After  2-3  minutes  add  10  ccm.  of  hypo 
and  shake.     What  is  the  difference  between  the  results 
in  (2)  and  (3)  ?     What  is  the  precipitate  in  (3)  ? 

EXP.  75.    EFFECT  OF  OXIDATION  ON  THE  PROPERTIES 
OF  ELEMENTS 

Materials.  Solutions  of  chromium  sulfate,  Cr2(SO4)3; 
sodium  chromate,  Na2CrO4;  potassium  permanganate, 
KMnO4;  manganese  sulfate,  MnSO4;  barium  chlorid, 
BaCl2;  lead  nitrate,  Pb(NO3)2;  oxalic  acid,  H2C2O4. 
Alcohol,  C2H6OH.  Sodium  peroxid,  Na2O2.  Lead  di- 
oxid,  Pb02.  NaOH.  HC1.  HNO3.  H2SO4.  Acetic 
acid,  H(C2H3O2). 

Procedure,     (a)    Chromium  compounds. 

1.  Add  NaOH  to  10  ccm.  of  Cr2(SO4)3  and  describe 
the  precipitate  of  Cr(OH)3  which  forms.  Dissolve  a 
little  of  it  in  HC1  and  in  HNO3.  In  the  compounds 


EXPERIMENTS  133 

formed,  is  chromium  acting  as  a  base-former  or  an  acid- 
former?  (The  color  of  these  compounds  sufficiently  indi- 
cates the  base-forming  condition  of  chromium.) 

2.  Treat  most  of  the  Cr(OH)3  with  2-3  g.  of  Na2O2, 
add  20  ccm.  of  water  and  boil.     The  color  produced  is  a 
sufficient  indication  that  chromium  is  acting  as  an  acid- 
former. 

3.  To  5  ccm.  of  the  solution  from  (2)  add  NaOH.     Is 
there     any   precipitate    now?     Why?     Add   BaCl2   and 
Pb(NO3)2  to  separate  5  ccm.  portions  of  the  solution  and 
make  just  acid  with  acetic  acid.     Describe  the  precipitates 
of  BaCrO4  and  PbCrO4  which  form.     Either  precipitate 
is  a  test  for  chromates.     The  same  reactions  may  be  used 
as  tests  for  barium  and  lead.     State  how. 

4.  Add  10  ccm.  of  cone.  HC1  and  5  ccm.  of  alcohol  to 
the  rest  of  the  solution  from  (2),  boil  and  note  change  of 
color.     What  does  it  indicate?     Write  equations  for  all 
the  reactions  which  have  taken  place. 

(6)   Manganese  compounds. 

1.  Add   NaOH    to   5   ccm.    of    MnSO4   and   describe 
the  precipitate  of  Mn(OH)2  which  forms.     Try  to  dis- 
solve a  little  in  HC1  and  in  NaOH.     Result?     In  these 
compounds  is  manganese  acting  as  an  acid-former  or  a 
base-former  ? 

2.  Dilute  10  ccm.  of  dilute  HNO3  with  an  equal  volume 
of  water,  add  some  Mn(OH)2  and  2-3  g.  of  lead  dioxid 
and  boil  5  minutes.     Allow  the  PbO2  to  settle  and  note 
the  color  of  the  solution,  which  is  sufficient   indication 
that  manganese  is  acting  as  an  acid-former. 

3.  To  5  ccm.  of  KMnO4  solution  add  5  ccm.  of  H2SO4 
and  oxalic  acid  until  the  color  is  bleached.     Oxalic  acid 
is  a  reducing  agent.     What   has   happened  to  the  per- 
manganate ?     Add  NaOH  to  the  bleached  solution  until 


134        LABORATORY  MANUAL  IN  CHEMISTRY 

it  is  alkaline.     Is  Mn(OH)2  precipitated  now?     Why? 
Write  equations  for  all  reactions. 

How  does  oxidation  affect  the  properties  of  an  element  ? 
Redaction  of  a  compound  has  what  effect  on  its  properties? 

(<?)    Testing  water. 

To  15  ccm.  of  H2SO4  add  5  drops  of  KMnO4  and 
divide  into  three  test  tubes.  Fill  (1)  with  distilled 
water,  (2)  with  tap  water,  (3)  with  water  in  which 
flowers  or  grass  have  been  standing.  Heat  all  three  to 
boiling  and  allow  to  stand  10-15  minutes.  The  water  in 
(3)  contains  organic  matter ;  (1)  contains  none.  Does 
(2)  contain  organic  matter  ?  Water  containing  much 
organic  matter  is  not  wholesome.  ' 

The  water  analysis  may  be  continued  further  by  testing 
it  for  chlorids  (p.  57),  sulfates  (p.  Ill),  and  "hardness" 
with  soap  (p.  124).  The  presence  of  much  "chlorids" 
sometimes  indicates  contamination  by  sewage.  The  pres- 
ence of  sulfates  means  little  except  when  accompanied  by 
magnesium  and  calcium,  due  to  "hardness."  The  tests 
for  nitrates  and  ammonia  are  significant  but  can  not  be 
made  quickly  or  simply. 

EXP.  76.     BLUE  PRINTS  AND  THEIR  REACTIONS 

Materials.  Solutions  of  ferric  chlorid,  FeCl3;  ferrous 
sulfate,  FeSO4*;  potassium  ferricyanid,  K3(FeC6N6)*; 
potassium  ferrocyanid,  K4(FeC6N6);  potassium  thiocya- 
nate,  KSCN ;  oxalic  acid,  H2C2O4 ;  hydrogen  peroxid, 
H2O2.  Cone.  HC1.  Chlorin  water,  C12.  Shingle  nails 
or  tacks.  Smooth-surfaced  letter  paper.  Cotton. 

Apparatus.     Test  tubes.     Glass  plate. 

*  Solutions  of  FeSO4  and  K8(FeC6N6)  must  be  freshly  prepared. 


EXPERIMENTS  135 

Procedure,     (a)  Ferric  salts. 

Add  5  com.  of  ferric  chlorid  solution  and  5  drops  of 
cone.  HC1  to  10  ccm.  of  water  and  divide  into  3  test  tubes. 
To  (1)  add  a  drop  of  potassium  ferricyanid,  to  (2)  potas- 
sium ferrocyanid ;  to  (3)  potassium  thiocyanate.  Note 
and  record  your  results. 

(£)  Ferrous  salts. 

Add  5  drops  of  cone.  HC1  to  5  ccm.  of  ferrous  sulfate 
/  solution,  dilute  with  10  ccm.  of  water  and  divide  into  3 
test  tubes.  To  (1)  add  a  drop  of  potassium  ferrocyanid ; 
to  (2)  potassium  ferricyanid ;  and  to  (3)  potassium  thio- 
cyanate. Note  and  record  your  results. 

Because  of  its  ready  oxidation  even  by  the  air,  it  is 
almost  impossible  to  get  a  ferrous  solution  free  from  ferric 
ions.  Pure  ferrous  solutions  give  colorless  test  in  (1)  and 
(3).  Explain  your  results. 

The  preceding  reactions  are  used  as  tests  for  iron ;  (a) 
2  and  3  being  used  for  the  ferric  condition  and  (b)  2  for 
the  ferrous  condition. 

(<?)    Change  from  ferrous  to  ferric. 

Pour  2  ccm.  of  ferrous  sulfate  into  a  test  tube,  add  5 
ccm.  of  chlorin  water  or  hydrogen  peroxid,  and  heat  to 
boiling.  Test  a  drop  of  the  solution  for  ferrous  and  ferric 
iron;  if  the  former  is  still  present,  add  more  oxidizing 
agent  and  boil  again.  Explain  what  has  happened  and 
write  equations  to  express  the  change,  assuming  that  you 
used  ferrous  chlorid  instead  of  sulfate. 

(c?)   Change  from  ferric  to  ferrous. 

1.  Pour  5  ccm.  of  cone.  HC1,  2  ccm.  of  ferric  chlorid 
solution,  and  10  ccm.  of  water  into  a  test  tube,  add  4-6 
shingle  nails  and  allow  to  stand  for  some  time,  testing  a 
few  drops  every  5  minutes  for  ferrous  and  ferric  iron  until 


136        LABORATORY  MANUAL  IN  CHEMISTRY 

the  latter  disappears.     Explain  what  has  happened  and 
write  equations  expressing  the  change. 

In  a  room  that  can  be  darkened  considerably,  mix  10 
com.  of  each  of  the  following  solutions :  ferric  chlorid, 
potassium  ferricyanid,  and  oxalic  acid. 

2.  To  5  ccm.  of  the  solution  add  10  ccm.  of  water  and 
see  if  you  have  any  test  for  ferrous  iron.     Let  this  test 
tube  stand  in  the  dark  until  the  end  of  the  exercise,  then 
note  again. 

3.  Put  5  ccm.  of  the  solution  in  a  test  tube  and  stand 
in  the  direct  sunlight  for  10-15  minutes,  then  dilute  with 
water.     Do  you  get  any  test  for  ferrous  iron  ?     What  has 
happened  to  the  ferric  iron  ?     Oxalic  acid  is  a  reducing 
agent.     Can  you  explain  ?     Does  this  change  take  place 
in  the  dark  ? 

4.  Dip  a  wad  of  cotton  in  the  solution  and  squeeze  al- 
most dry.     Rub  a  sheet  of  writing  paper  with  the  moist- 
ened cotton,  coating  one  side  evenly  and  lightly,  then  place 
in  a  dark  drawer  to  dry.     Lay  the  paper  on  a  book,  place 
some  opaque  object  upon  it  and  expose  it  to  the  sun  until 
the  paper  assumes  a  bronze  color.     If  a  fern,  flower,  or 
head  of  grass  is  used,  cover  with  a  glass  plate  to  get  sharp 
outlines.     Wash  the  print  in  water  2-3  times,  dip  for  a 
minute  into  very  dilute  HC1,  wash  again,  dry  and  put  into 
your  notebook.     What  is  the  compound  on  the  paper  ? 

EXP.  77.    IDENTIFICATION  OF  SIMPLE  SUBSTANCES 

Materials.     Water-soluble  salts  of  the  different  metals. 

(a)  Determination  of  the  metal. 

Dissolve  most  of  the  salt  (Always  keep  some  for  refer- 
ence) in  water.  Lay  a  sheet  of  white  paper  on  the  desk 
and  over  it  place  a  piece  of  clean  glass.  With  a  glass  rod 


EXPERIMENTS  137 

put  5-10  drops  of  the  solution  in  different  places  on  the 
glass.  Dip  a  clean  glass  rod  into  NaOH  and  touch  the 
edge  of  one  of  the  drops  with  it.  Note  any  action.  In  a 
similar  way  test  other  drops  of  the  solution  with  NH4OH, 
(NH4)2S,  and  K2CrO4.  Using  the  Table  and  notes  for 
help,  draw  inferences  as  to  the  metal  present  in  your  solu- 
tion. Confirm  your  inferences  by  making  the  tests  for 
that  metal  given  elsewhere  in  the  manual.  If  no  indica- 
tion is  obtained,  examine  the  flame,  heat  on  charcoal  with 
Na2CO3,  and  make  test  for  NH4.  What  metal  is  present 
in  the  compound  you  have?  How  do  you  know? 

(6)  Determination  of  the  acid. 

If  any  metal  other  than  potassium,  sodium,  and  ammo- 
nium has  been  found,  make  the  remainder  of  your  solution 
alkaline  with  Na2CO3  *  solution,  boil  for  10  minutes,  then 
filter.  Acidify  1-2  ccm.  of  the  nitrate  with  HNO3  and 
test  for  HC1.  If  the  test  is  negative,  acidify  the  whole 
filtrate  with  HC1  and  boil  to  decompose  the  carbonate, 
noticing  whether  H2S  or  any  other  gas  which  you  can 
recognize  by  the  odor  is  liberated.  Using  1-2  ccm.  por- 
tions of  this  boiled  solution,  make  tests  for  the  other  acids 
which  may  be  present,  referring  to  the  statement  of  Solu- 
bilities, to  ascertain  which  acids  are  possible.  Make  the 
test  for  carbonates  (if  necessary)  on  some  of  the  dry  sub- 
stance. What  acid  radicle  is  present  in  the  compound 
which  you  have?  How  do  you  know? 

Boiling  with  Na2CO3  transforms  the  salt  which  you 
had  into  a  sodium  salt  of  the  same  acid  and  precipitates 
the  metal  as  a  carbonate,  as  the  following  typical  equation 
shows : 

2  AgNO3  +  Na2CO3  ->  Ag2CO3  +  2  NaNO3. . 
*  This  sodium  carbonate  must  be  the  purest  obtainable. 


138        LABORATORY  MANUAL  IN  CHEMISTRY 


PRECIPITATES  PRODUCED  BY 

COLOR 
OF  SALTS 

K,Cr04 

(NH4)2S 

NH4OH 

NaOH 

red 
red 

yellow 

black 
black 
black 
black 

black 
white 
white 

brown 
yellow 
yellow 
white  l 

white 
yellow 
white 
white 

Ag 
Hg  ous 
Hgic 
Pb 

yellow 
olive 

brown 
black 
yellow 

white 
blue1 
white1 

white 
blue 
white 

white 
blue 
white 

Bi 
Cu 
Cd 

yellow  2 
orange  2 
brown  2 
yellow  2 

white 
white 
white 

white1 
white  l 
white1 

white 
white 
white 
white 

As 

Sb 
Sn  ous 
Sn  ic 

white 
gray 
black 
black 

white 
gray 
green 
red 

white  x 
gray 
green 
red 

white 
green 
green 
reddish 

Al 
Cr 
Fe  ous 
Feic 

black 
black 
buff 
white 

pink1 
green  l 
buff 
white  l 

lavender 
green 
buff 
white  l 

red 
green 
pink 
white 

Co 
Ni 
Mn 
Zn 

yellow 

white 

white 

white 
white 
white 
white 

Mg 
Ba 
Sr 
Ca 

white 
white 
white 

K 

Na 
NH4 

1  Soluble  in  excess. 

2  Sometimes  difficult  to  obtain;  add  drop  of  HC1  also. 

SOLUBILITY  OF  COMPOUNDS 

Potassium,  sodium,  and  ammonium  compounds  all  soluble  in  water. 

Nitrates  and  acetates  all  soluble. 

Chlorids  all  soluble  except  silver,  mercury  (ous),  and  lead. 

Sulfates  all  soluble  except  barium,  strontium,  calcium,  and  lead. 

Carbonates,  phosphates,  and  borates  all  insoluble  except  potassium, 
sodium,  and  ammonium  salts. 

Oxids  and  hydroxids  and  sulfids  all  insoluble  except  potassium, 
sodium,  ammonium,  barium,  strontium,  and  calcium. 


LISTS  OF  CHEMICALS  AND  SUPPLIES 


A  liberal  allowance  for  a  class  of  10  students  doing  all  the  experiments. 
All  chemicals  are  C.  P. 


lib.  Acid,  acetic,  30% 
12  Ib.  Acid,  hydrochloric,  Sp.  Gr. 

1.19 

6  Ib.  Acid,  nitric,  Sp.  Gr.  1.42 
1  Ib.  Acid,  oxalic 
8  Ib.  Acid,  sulfuric,  Sp.  Gr.  1.84 
2qt.  Alcohol,  95% 

1  oz.  Alizarin 

2  Ib.  Alum 

1  oz.  Aluminum,  sheet 

8  oz.  Aluminum  sulfate 

1  Ib.  Ammonium  carbonate 

1  Ib.  Ammonium  chlorid 
10  Ib.  Ammonium    hydroxid,     Sp. 
Gr.  0.9 

1  oz.  Ammonium  molybdate 

1  Ib.  Ammonium  nitrate 

1  oz.  Antimony  chlorid 

1  oz.  Antimony  oxid 

1  oz.  Arsenious  oxid 

8  oz.  Barium  chlorate 

8  oz.  Barium  chlorid 

8  oz.  Barium  nitrate 

1  oz.  Bismuth  chlorid 

1  oz.  Bismuth  oxid 

8  oz.  Bromin 

1  oz.  Cadmium  nitrate 

1  Ib.  Calcium  carbid 
10  Ib.  Calcium    carbonate,   marble 
chips 

8  oz.  Calcium  carbonate   precipi- 
tated chalk 

1  Ib.  Calcium  chlorid,  granules 

1  Ib.  Calcium    fluorid,    fluorspar, 

powder 
8  oz.  Calcium  nitrate 

2  Ib.  Calcium  oxid,  lime,  in  tins 
1  Ib.  Calcium  sulfate,  gypsum 


2  Ib.  Calcium  sulfate,  plaster  of 
Paris 

1  Ib.  Carbon  disulfid 

1  oz.  Cochineal,  ground 

1  Ib.  Charcoal,  animal.  Bone- 
black. 

I  Ib.  Charcoal  wood 

1  Ib.  Charcoal  wood  blocks 

1  Ib.  Chloride  of  lime 

1  Ib.  Chloroform 

4  oz.  Chromium  sulfate 

4  oz.  Cobalt  chlorid 

4  oz.  Cobalt  nitrate 

1  oz.  Congo  red 

1  Ib.  Copper,  foil,  ^  in. 

2  Ib.  Copper  turnings 

4  spools  Copper  wire,  Nos.  16,  18, 

24,  30. 
1  oz.  Copper  oxid,  black  powder 

3  Ib.  Copper  sulfate 
1  Ib.  Ether 

1  oz.  Fehling's  solution  tablets 
15  packs  Filter  papers,  4  in. 

2  packs  Filter  papers,  6  in. 
1  pack  Filter  papers,  12  in. 
1  oz.  Hydrochinon 

1  oz.  Indigo 

4  oz.  lodin,  resublimed 

1  Ib.  Iron  powder  "alkoholized  " 

2  spools  Iron  wire,  Nos.  16  and  24 
1  Ib.  Iron  chlorid  (ic) 

1  Ib.  Iron  sulfate  (ous) 

2  Ib.  Iron  sulfid  (ous)  for  H2S 
1  Ib.  Lead,  sheet 

8  oz.  Lead,  acetate' 
4  oz.  Lead  dioxid 
1  Ib.  Lead  nitrate 
1  Ib.  Lead  oxid,  litharge 


139 


140        LABORATORY  MANUAL  IN  CHEMISTRY 


1  oz.  Litmus  cubes 

25  books  Litmus  paper,  red 
25  books  Litmus  paper,  blue 

4  oz.  Logwood,  ground 

4  oz.  Magnesium,  ribbon 

8  oz.  Magnesium  nitrate 

4  oz.  Magnesium  oxid,  wet  process 

8  oz.  Magnesium  sulfate 

2  Ib.  Manganese  dioxid,  powdered 
8  oz.  Manganese  nitrate 

8  oz.  Manganese  sulfate 

]  Ib.  Mercury 

4  oz.  Mercury  chlorid  (ic) 

4  oz.  Mercury  nitrate  (ic) 

4  oz.  Mercury  nitrate  (ous) 

4  oz.  Mercury  oxid 

4  oz.  Nickel  sulfate 

1  Ib.  Oxone.     (Fused  sodium  per- 

oxid) 

1  oz.  Phenolphthalein 
1  oz.  Phosphorus,  red 
4  oz.  Phosphorus,  yellow 
1  oz.  Phosphorus  pentoxid 
1  oz.  Potassium,  metal 
8  oz.  Potassium  bromid 
8  oz.  Potassium  carbonate 

3  Ib.  Potassium  chlorate 
1  Ib.  Potassium  chlorid 

4  oz.  Potassium  chromate 

1  Ib.  Potassium  dichromate 
8  oz.  Potassium  ferricyanid 
4  oz.  Potassium  ferrocyanid 

1  oz.  Potassium  acid  sulfate 

2  Ib.  Potassium  hydroxid,  sticks 
2  Ib.  Potassium  nitrate 


4  oz.  Potassium  iodid 

4  oz.  Potassium  nitrite 

8  oz.  Potassium  permanganate 

8  oz.  Potassium  sulfate 

1  oz.  Potassium  thiocyanate 

1  Ib.  Rochelle  salt 

4  oz.  Silver  nitrate 

4  oz.  Sodium,  metal 

4  oz.  Sodium  acetate 

1  Ib.  Sodium    carbonate,    purest, 

dry 

5  Ib.  Sodium  chlorid,  fine 
4  oz.  Sodium  chromate 

2  Ib.  Sodium  hydroxid,  sticks 

1  Ib.  Sodium  nitrate 
4  oz.  Sodium  nitrite 

4  oz.  Sodium  peroxid,  powder 
8  oz.  Sodium  phosphate 

2  Ib.  Sodium  sulfate,  crystals 
8  oz.  Sodium  sulfite,  crystals 

2  Ib.  Sodium  thiosulfate,  hypo 
8  oz.  Strontium  chlorate 

4  oz.  Strontium  chlorid 

3  Ib.  Sulfur 

1  oz.  Tartar  emetic 
1  Ib.  Tin,  granulated 
8  oz.  Tin  chlorid  (ous) 
1  oz.  Tin  oxid  (ic) 
1  sheet  Turmeric  paper 
1  Ib.  Zinc,  dust 

3  Ib.  Zinc,  mossy 
1  Ib.  Zinc,  sheet 

4  oz.  Zinc  nitrate 

4  oz.  Zinc  oxid,  wet  process 
8  oz.  Zinc  sulfate 


MATERIALS  TO  BE  OBTAINED  LOCALLY  AS  NEEDED 


4  oz.  Baking  powders,  several  dif- 
ferent kinds 
1  Ib,  Baking  soda 
1  pt.  Benzine 
4  oz.  Beans 


Blue  print  paper 

1  Ib.  Borax 

4  doz.  Candles,  Christmas 

2  Carbonated  water,   syphons  or 

bottles 


INDIVIDUAL  APPARATUS 


141 


4  oz.  Cheese 

10  yd.  Cheesecloth  (towels) 

4  oz.  Coal  (soft) 

4  oz.  Corn  meal 

4  Ib.  Cotton  batting 

|  yd.  Cotton  cloth,  colored. 

|  yd.  Cotton  cloth,  white 

4  oz.  Cream  of  tartar 

1  Egg,  raw 

1  Egg,  hard  boiled 

4  oz.   Fertilizers,  several  different 

kinds 
4  oz.  Flour 

Fruit 

4  oz.  Glucose  sirup 
4  oz.  Hydrogen  peroxid 
1  box  Iron  picture  wire 
1  Ib.  Iron  shingle  nails 
1  pt.  Kerosene 
4  oz.  Lard 

Matches,  parlor 

Matches,  sulfur 


4  oz.  Meat 

4  oz.  Milk 

4  oz.  Nuts 

1  pt.  Olive  oil 

1  Ib.  Paraffin 

4  oz.  Peas 

1  Ib.  Rock  candy 

10  sheets  Paper,  black 

10  sheets  Paper,  writing 

1  Potato 

4  oz.  Starch 

1  cake  Soap 

1  pt.  Turpentine 

1  Ib.  Sugar,  dark  brown 

1  Ib.  Sugar,  granulated 

Vegetables 
4  oz.  Vinegar 
1  oz.  Wool  or  felt 

4  oz.  Washing  powder,  several  dif- 

ferent kinds 

5  Ib.  Washing  soda 
3  Yeast  cakes. 


INDIVIDUAL  APPARATUS 

For  class  of  10  students.    Liberal  allowance  for  breakage  has  been  made. 


12  Beakers,  500  ccm. 
24  Beakers,  250  ccm. 

24  Beakers,  125  ccm. 
12  Brashes,  test  tube 

15  Burners,  Bunsen  with  wing  tips 
12  Calcium  chlorid  tubes,  straight, 

1  bulb 

12  Capsules  for  sodium  (see  p.  x) 
12  Clamps  for  condensers 
12  Clamps  for  test  tubes 
12  Condensers  (Liebig),  15  in. 
12  Combustion  spoons,  \  in.  bowl 
15  Crucibles,  porcelain,  No.  0,  with 

covers 

25  Dishes,  evaporating,  No.  1 
12  Dishes,  lead 

12  Files,  3-cornered 


5  packs  filter  paper,  9  cm. 

5  packs  filter  paper,  15  cm. 

12  Flasks,  flat  bottom,  500  ccm., 

with  2-hole  rubber  stoppers  to  fit 
25  Flasks,  flat  bottom,  250  ccm., 

with  2-hole  rubber  stoppers  to  fit 
12  Flasks,  round  bottom,  500  ccm., 

with  1-hole  rubber  stoppers  to  fit 
12  Flasks,  round  bottom,  250  ccm., 

with  1-hole  rubber  stoppers  to  fit 
12  Frying  pans,  iron,  5  in. 
12  Funnels,  2|  in. 
5  doz.  Fruit  jars,  pint 
50  Glass  plates,  3  x  3  in. 
12  Glass  plates,  6  x  6  in. 
10  Glass  plates,  3  x  4  in.     Cobalt 

glass 


142   LABORATORY  MANUAL  IN  CHEMISTRY 


100  ft.  Glass  tubing,  6  mm.  outside 

diameter.     For  bending 
25  ft.  Glass  tubing,  3   mm.  outside 
diameter.   For  stirring  rods. 
12  Graduates,  25  com. 
12  Medicine  droppers 
12  Mortars  with  pestles,  porcelain, 

4  in. 

12  Pincers,  iron,  4  in. 
12  Pipe  stems,  clay 
15  Pipe  stem  triangles,  small 
12  Pneumatic  troughs  (see  p.  vii) 
12  Retorts,  125  com.,  with  ground 

glass  stoppers 


50  ft.  Rubber  tubing,  T3g  in.  inside 

diameter 

12  Stand  irons  with  2  rings 
20  doz.  Test  tubes,  soft,  6  x  f  in. 
20  Test  tubes,  side-neck,  6  x  f  in. 

12  1-hole  rubber  stoppers  to  fit 
24  Test  tubes,  ignition,  6  x  f  in. 
12  Test-tube  holders,  brass  wire 
12  Test-tube  racks  for  12  test  tubes 
15  Thistle  tubes,  10  x  ^  in. 
20  Wire  gauze,  5  x  5  in. 


APPARATUS  FOR  GENERAL  USE 


1  doz.  Asbestos  sheets 

2  Balances,      platform,      weights 
500  g.  to  1  g. 

5  Balances,  horn  pan,  7  in.  beam 

weights  100  g.  to  0.01  g. 
1  Barometer 

5  Beakers,  1000  com. 

3  Dry  cells 

4  Bottles,  2  liter  (Acid  bottles) 

12  Bottles,  ground  glass  stoppers, 

1  liter 
100  Bottles,  ground  glass  stoppers, 

250  ccin. 

50  Bottles,  salt  mouth,  8  oz. 
10  Bottles,  salt  mouth,  16  oz. 
4  Burettes,  50  com.,  graduated 
1  Combustion  furnace      ] 
15  ft.  Combustion  tub-  ^  19 

ing,  1  cm.  inside  diam.  J  ai 
1  set  Cork  borers  (6  in  set) 
1  gross  Corks,  assorted 

1  Eudiometer  and  standard,   coil 
and  mercury   (10  Ib.)    Exp.  33 

2  Dishes,  evaporating,  6  in. 

1  Dish,  evaporating,  10  in. 

2  Files,  round 

6  Flasks,  flat  bottom,  1000  com.,  1- 
and  2-hole  rubber  stopper  to  fit 


4  Funnels,  glass,  4  in. 
1  Funnel,  glass,  6  in. 

3  Gas  measuring  tubes,  graduated, 
12  in.  long,  |  in.  inside  diameter 

4  Gas  measuring  tubes,  not  gradu- 
ated,  12  in.   long,   £  in.  inside 
diameter 

1  Gas  pipe,  iron,  20  x  £  in. 

2  Graduates,  1000  com. 

2  Graduates,  500  com. 
4  Graduates,  100  com. 

1  Hammer 

3  Lamp  chimneys  (student) 

2  Magnets 

2  Magnifying  glasses 

1  Mortar  and  pestle,  iron,  6  in. 

2  Pinch  cocks,  Mohr's,  medium 
2  Pipettes,  100  com. 

2  Pipettes,  20  ccm. 

6  Plates,  porcelain,  6  in.     (Buy  in 

crockery  store) 

Platinum  foil,  T^57  in.,  2  sq.  in. 
Platinum  wire,  No.  27,  25  in. 
2  Ib.  Rubber  stoppers,  1  and  2  hole, 

Nos.  0-5 

2  Separating  funnels,  100  ccm. 
2  Thermometers,  0-200° 


NOTE    ON    APPARATUS    AND    CHEMICALS      143 


NOTE   ON  PURCHASING  APPARATUS  AND  CHEMICALS 

The  preceding  lists  of  apparatus  and  chemicals  include  everything 
needed  for  a  class  of  ten  students  working  individually  and  performing 
all  the  experiments,  and  for  all  the  instructor's  experiments,  in  a  school 
where  chemistry  has  never  been  taught  before.  For  the  second  and  all 
subsequent  years,  the  lists  may  be  greatly  cut  down.  The  quantities  of 
chemicals  specified  will  last,  in  many  instances,  several  years.  It  is  not 
economical  to  buy  in  smaller  quantities,  however,  because  the  prices 
charged  are  proportionately  much  higher.  With  careful  handling,  much 
of  the  apparatus  for  general  use  need  never  be  replaced. 

The  attention  of  instructors  in  schools  handicapped  by  lack  of  funds  is 
called  to  the  following  suggestions  for  minimizing  the  expense  for  chemi- 
cals and  apparatus.  When  unusual  or  expensive  apparatus  is  called  for 
in  the  Manual,  suggestions  for  substituting  other  materials  are  frequently 
made  (see  p.  x,  xi,  xii,  13,  16,  21,  26,  28,  32,  40,  69).  The  barometer, 
thermometers,  dry  cells,  induction  coil  and  mercury  may  be  borrowed 
generally  from  the  physics  department  (possibly  the  eudiometer,  also). 
Test-tube  racks  may  be  constructed  in  the  manual  training  department. 
Lead  dishes  may  be  made  out  of  sheet  lead  ;  blowpipes  from  glass  tubing 
(see  p.  91). 

For  satisfactory  results,  Exp.  47  requires  a  combustion  furnace,  useful 
also  in  Exp.  16  a.  By  omitting  Exp.  47  and  (if  the  apparatus  cannot  be 
borrowed  or  devised  from  available  material)  Exps.  16  a  and  33,  a  rela- 
tively great  saving  can  be  effected.  Condensers  and  clamps  to  hold  them 
are  relatively  expensive  and  are  used  only  in  Exps.  21  and  61.  By  hav- 
ing students  use  this  apparatus  in  turn,  the  number  may  be  cut  down  to 
three  if  necessary  (or  entirely  eliminated,  see  p.  40) .  Similarly,  six  re- 
torts may  be  made  to  serve  for  Exp.  36.  Though  it  is  not  recommended, 
students  may  work  in  pairs.  Much  of  the  apparatus  listed  for  general 
use  is  for  the  instructor's  use  and  convenience  about  the  laboratory.  It 
is  possible,  however,  to  get  along  with  one  half  of  the  bottles,  evaporating 
dishes,  funnels,  gas  measuring  tubes  and  graduates  mentioned  in  this  list. 

If  all  the  above  devices  are  adopted,  a  saving  of  from  one  half  to  one 
third  of  the  cost  of  the  lists  as  printed  may  be  accomplished.  This 
apparent  saving  will  be  at  the  expense  of  the  instructor,  from  whom  addi- 
tional labor  will  be  necessitated.  It  is  to  be  regarded  as  doubtful  econ- 
omy, for  the  efficiency  of  his  teaching  is  likely  to  be  lessened  thereby. 


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